Well, for one thing, the kind of ‘universalism’ being aimed against by such retorts (which I expect are entirely rhetorical, though not very well thought out rhetoric) is a kind that has no place for the wrath of God. Which isn’t orthodox/evangelical universalism at all.
I do find it very difficult sometimes to get opponents to even admit that I affirm the wrath of God and stress that salvation must be from sin. They imagine that I am one of those unorthodox universalists who want to license whatever it is they happen to want to be doing without penalty so long as it feels pleasant to them and isn’t obviously hurting anyone else. I can’t say those opponents are wrong to protest against that kind of universalism, but it’s frustrating sometimes when they insist on lumping me in with that kind.
There is no salvation from sin without the grace of God, and that has to be ontologically primary (by which I mean that if God doesn’t intend and act to save someone from sin, that person is not going to be saved from sin, period.) But there is also no salvation from sin without repentance by the person. Those who love and practice their lying, sorcery, murdering, adultery and any other item on the various injunctive lists (and keep in mind that God considers things like murder and adultery to cover a much broader scope than we might be comfortable imagining!), will not be entering the kingdom. God and the saints will always be encouraging repentance from sin, but God has no problem making it hot (so to speak) for people until they repent.
Also, though, I agree with the concerns by people who face this kind of opposition: there is no other righteousness but God’s righteousness (as St. John says in his first epistle), and God is not going to let us off with being anything less than righteous. But we shouldn’t be trying to be righteous simply to escape punishment; that’s what wicked and lazy slaves do! Not members of the family. I suspect that unorthodox notions of ‘imputed righteousness’ also lurk in the background behind this stance: i.e., the notion that God will simply pretend we are righteous and so treat us as though we are righteous, without actually leading us to be righteous.