It sure isn’t my place to judge their hearts and their underlying intentions! – or if I do, to make as charitable a guess as I can, often from scanty evidence.
A lot of people believe that salvation comes from, or is exhibited by, having the proper beliefs (which is gnosticism). And that’s naturally going to lead to those people thinking their own salvation from eternal conscious torment or from annihilation is at stake, and the salvation of other people, if they don’t resist as hard as they can. As I like to say, in their defense (even in defense of non-Christians who are like that, such as Muslim terrorists), no one is tolerant of Ebola, and in principle they shouldn’t be.
So for Arminianistic Christians in that condition, they want to make sure they’ve properly convinced God to save them from final perdition (or that they’ve properly convinced the Son to convince the Father to spare them from perdition 
), and depending on how hardcore they are as Arms they may want to make sure they keep convincing God to spare or save them from hell. If they think they do this by right beliefs, and if they think final perdition is a right belief, they’ll be easily belligerent about opposing Christian universalism, as much so as about opposing any kind of Calvinism (since that denies and opposes the gospel assurance they protect: the total scope of God’s intention to save sinners from sin.)
For Calvinistic Christians in that condition, they want to make sure about whether they’re among God’s elect or not. They don’t believe they have to earn God’s salvation, or to earn God’s persistence in saving them, and they have the important gospel assurance of God’s original continuing persistence to save whomever He intends to save. But they reject the Arminian assurance that God definitely means to save everyone which certainly would include themselves even if they happen not to feel that way at the moment. Moreover, for a Calvinist, especially a harder core Calv, there is a strong practical reason to identify the non-elect, because those people must be wholly evil (if a person has any true good at all, that would be evidence of the action of the Holy Spirit in their lives, and so be evidence that God intends to save them from sin), and so on this theory can be properly hated and opposed to the fullest strength, just like God chooses to do (on this theory). Even aside from this leading to vast uncharity toward the non-elect opponent, it’s simply a matter of protecting one’s self, and one’s loved ones, from people who will only cause harm to other people. So identifying the non-elect, if possible (except it isn’t really possible in principle, since God might be waiting to start leading them to repentance later), is just as important though for different reasons as identifying the elect if possible (except it isn’t really possible in principle, since anyone may mistakenly believe anyone is of the elect, even the non-elect believing themselves to be of the elect.) Looking hard for that assurance which Arminians have and they lack, Calvinists may easily latch onto the idea that right doctrine is evidence of election, and even that wrong doctrine is evidence of non-election (though the two ideas are quite distinct and don’t necessarily entail each other). Being gung-ho about standing for final perdition thus helps serve as reassurance that they are, or may probably be, among the elect, instead of among the hopelessly non-elect whom God never shall choose to save from final perdition; and someone’s belief against final perdition may (on this theory) be evidence of them being of the non-elect. Especially since false teachers are strongly condemned in the scriptures to post mortem punishment, and they see little evidence at best that false Christian teachers, identified as such, are ever expected to repent and be saved. (And any such evidence pointed out to them, such as Paul’s expectations about handing over various false Christian teachers to punishment, even to death, but so they will learn better and be surely saved, would contradict apparent evidence they previously accepted in favor of final perdition! – which could easily lead to unraveling more such evidence as principles are applied forward. So that’s a threat which they’ll strongly resist acknowledging.)
Let me stress: neither such Christian is being evil by doing this. They’re compounding a few doctrinal errors (which they don’t recognize as such) with some panic over them and/or other ‘good’ (or at least loved) people being threatened with the worst possible end for anyone. They can easily be led into uncharity and injustice this way, but the underlying problem isn’t a heart insistence on denying God’s salvation of their enemies. They can be led by this situation into that eventually, but the original problem isn’t their own evil desire against other people.
Now, I say this not only in their defense, but also because I know some people do not only have such desires but intentionally foster them, and without the excuses these people have.
I know that because I was that kind of person: the kind who didn’t have any kind of misguided intention of protecting good people, or loved people, or even myself, from the worst possible end. Nor did I have any kind of psychological damage from being abused by other people which might emotionally excuse my hatred as a cross I had to bear and from which I should be healed someday. I just hated my enemies and wanted to be able to hate at least some of them permanently, like AI opponents in a video game whom I could safely oppose as much as I wanted forever.
In my defense (if I may be allowed that), I didn’t hate my enemies very strongly; I was fine with God saving most people, even post-mortem (though for many years I couldn’t see any evidence of that). But I was also fine with God not saving some people and I didn’t really care much about the reasons why He didn’t (though me being me I naturally had reasons why He didn’t, which seemed like good reasons to me. 
)
I was the opposite of the Alexandrian goldsmith to whom, in the legend of the first Desert Father, the Holy Spirit brought St. Anthony the Great, to be taught what it means to be truly righteous – and to learn Christian universalism. I was comfortably sure I had done the right things to secure my own salvation, and aside from some people I happened to emotionally care about I didn’t really care whether others were saved or not. I didn’t care if they were, and I didn’t care if they weren’t. If most of the people outside in the street went finally to hell, that might be personally bothersome if I happened to care about some of them, but otherwise I didn’t mind. I was like St. Anthony in the legend.
But the Alexandrian goldsmith, who only prayed twice a day, once in the morning and once at night, and who unlike Anthony didn’t have a high opinion of his own righteousness, prayed only one thing: he gave thanks to God that God was so great and good that He would have no trouble at all saving all those other people, no matter how many they were, no matter how evil they were – but he worried that even God might have some trouble to save such a sinner as himself.
I only read that legend many years after coming to believe that I ought to believe God can and will save all sinners from their sins. But I remember reading that legend the first time and sympathizing with what St. Anthony must have felt (in whatever history lay behind the legend) as he wailed in grief and awe and tore his clothes: IT IS TRUE, IT IS TRUE, I AM NOT EVEN AS RIGHTEOUS AS A GOLDSMITH IN ALEXANDRIA!!
Because that’s how I felt when I started to realize I ought to accept in my heart that Jesus will not deny the name of Jesus. But that all that time, in my heart, I had been denying the name of Jesus. And as I studied the scriptures harder and more carefully, I came to see that whereas I had thought I was like the apostles, I not only had been like the Pharisees, but I had been like the apostles in the wrong ways (in which they were like the Pharisees!) I should have been putting myself penitently in the place of the Pharisees, and the rebuked apostles. I had been blithely agreeing with all those judgments of Jesus, because obviously that was the right thing to do to be on Jesus’ side, and I even noticed that Jesus often set up His opponents the way Nathan set up King David when telling his parable.
I just didn’t notice I was King David. “THOU ART THE MAN!”
So, yeah, such people exist, and I was one of them. I know what Saul of Tarsus felt when he thought he was being righteous, and really was being righteous in many real and important ways – and yet all along was the chief of sinners, no better than Satan.
But I don’t like to make guesses about which people are such people, or to preach against them particularly. I would rather preach against myself. 
I look for real excuses for why those-non-universalists-over-there (or those other alt-Christians over there, or those other religious people over there, or those atheists and agnostics over there) behave they way they do.
I didn’t have their excuses. And I wouldn’t have their excuses if I went back to behaving that way.
Some of them, realistically, don’t have any more excuse than I did. But it isn’t my business to focus on figuring out who those people are.
)
