It always helps to read a passage in context, especially its immediate literary context.
3 We ought to give thanks to God always for you, brethren, as it is meet, because increase greatly doth your faith, and abound doth the love of each one of you all, to one another;
4 so that we ourselves do glory in you in the assemblies of God, for your endurance and faith in all your persecutions and tribulations that ye bear;
5 a token of the righteous judgment of God, for your being counted worthy of the reign of God, for which also ye suffer,
6 since [it is] a righteous thing with God to give back to those troubling you – trouble,
7 and to you who are troubled – rest with us in the revelation of the Lord Jesus from heaven, with messengers of his power,
8 in flaming fire, giving vengeance to those not knowing God, and to those not obeying the good news of our Lord Jesus Christ;
9 who shall suffer justice – destruction age-during – from the face of the Lord, and from the glory of his strength,
10when He may come to be glorified in his saints, and to be wondered at in all those believing – because our testimony was believed among you – in that day;
11 for which also we do pray always for you, that our God may count you worthy of the calling, and may fulfil all the good pleasure of goodness, and the work of the faith in power,
12 that the name of our Lord Jesus Christ may be glorified in you, and ye in him, according to the grace of our God and Lord Jesus Christ.
This passage is meant as an encouragement to the Thesalonian believers who were suffering persecution for their faith in Christ. It encourages them by affirming: 1) they will be rewarded for their faithfullness, and 2) the ones persecuting them will reap what they sow. And when the Lord returns, which this passage seems to assume would be soon, even in their life time, these persecutors will suffer a similar fate to that of Sodom and Gomorrah, destruction.
Paul warns of destruction, olethros, in 1 Thes. 5 also saying,
1 And concerning the times and the seasons, brethren, ye have no need of my writing to you,
2 for yourselves have known thoroughly that the day of the Lord as a thief in the night doth so come,
3 for when they may say, Peace and surety, then sudden destruction doth stand by them, as the travail [doth] her who is with child, and they shall not escape;
As well as in 1 Tim. 6:9
9 and those wishing to be rich, do fall into temptation and a snare, and many desires, foolish and hurtful, that sink men into ruin and destruction,
To me, destruction, olethros’ most evident meaning is the destruction that comes in this life due to sin. It’s not even speaking of punishment in the afterlife, but in this life. Paul even speaks of such destruction as resulting in one’s spirit being saved in 1 Cor. 5:5
5 to deliver up such a one to the Adversary for the destruction of the flesh, that the spirit may be saved in the day of the Lord Jesus.
I see no reason to read into these passages anything more than the destruction that comes into a person’s life in this life due to sin, especially the sin of persecuting the church.
It’s also significant to note that the word translated “shall suffer” or “punished”, katadike, in 2 Thes. 1:9 is also used in Jude 7:
7 as Sodom and Gomorrah, and the cities around them, in like manner to these, having given themselves to whoredom, and gone after other flesh, have been set before – an example, of fire age-during, justice suffering.
Not only is the destruction of Sodom and Gomorrah an example of such justice, punishment, but it also uses the word aionios to describe the fire that destroyed Sodom and Gomorrah. The cities were burnt to ash as judgment from God, but the fire did not last endlessly. In fact, I believe in 1 Thes. 1:9 that aionios is explained in the immediately following phrase, “destruction age-during – from the face of the Lord”. In other words, “from the face of the Lord” explains what Paul meant by “aionios”. Jesus’ appearance, showing His face, brings destruction to those who are not on His side and rewards to those who are.
To take this passage and “read into” it ECT or even annihilation is ludicrous. It does not speak of what happens in the afterlife, but what happens in this life as a result of persecuting the church. It was meant as a word of encouragement to the Thessalonians to remain faithful, trusing in God to bring vengence on those who were persecuting them. It is not meant to teach what happens in the afterlife. I neither affirms or denies punishment in the afterlife, but only affirms destruction in this life.