I've mentioned elsewhere how I wish Universalism were true, but the testimony of Scripture simply does not allow it to be. I've read universalist arguments, hoping to be convinced. But they simply don't stand up under scrutiny.
The core argument is a claim that the Greek words Aion and Aionion, which they say are translated incorrectly as "eternal", actually mean a fixed period of time, often a very long one but still one that will end. And thus Gehena/the Lake Fire being described as "eternal" doesn't make it permanent.
Here is the problem, it's only Aionion that is translated Eternal. Aion's meaning is what they say it is, it's where the English word Eon comes from, and can be viewed as a synonym for Age and Era, but the KJV also sometimes translates it World, however it is distinct from Kosmos.
Aionion is derived from Aion, but that doesn't mean it must also contain the "will end" element of it. It could be related like how Age is to Ageless, or End to Endless, or Time to Timeless.
I'm not a Greek expert, but I know this much. Aionion (translated as both Eternal and Everlasting) is not just used to describe how long the people sent to Gehena/Lake of Fire spend there. It's also used to describe the Life promised to those who Believe. We are promised we will NEVER die.
What they combine with that flawed Greek lesson is that Revelation 22:15 to them seems to describe those earlier sent into the Lake of Fire as now merely being locked outside of New Jerusalem. However those are in fact not the same group of people as I explain in my Outer Darkness study.
They will make a claim that all the Greek early Church Fathers unanimously believed in Universlaism, and it was translations into Latin that caused Aionion to start meaning Eternal. I have read some quotes of the early fathers that sound universalist, but I've already expressed why I don't view them as authoritative. It adds an amusing context to the desire enemies of Eternal Security have to point to the Church Fathers.
You may be thinking "aren't you by definition a believer in Eternal Security if you're a Universalist?" Technically no, a Universalist (a Christian one at least) still likely believes you're given the opportunity to avoid going to Gehenna even temporarily when you accept Jesus as your Savior. So they can therefore disagree among themselves on whether or not your get out of Gehenna free card can be forfeited.
Critics of Eternal Security probably fear that believing in Eternal Security is part of a slippery slop toward Unviersalism. But in truth the importance of defending the Biblical doctrine of Eternal Security is likely to have less resonance to a Universalist.
Universalisim is like any other works salvation in a sense. They believe even those who go through the Lake of Fire are Saved because of Jesus. So they are saying that what Jesus suffered sometimes needs to be added to. The role of the Lake of Fire in Universalism is not unlike Salvation by works. It also suggests the completed work of Jesus on the Cross sometimes needs to be added to.
If any universalist who sees this thinks they can refute my arguments, please, I invite you to leave a comment, brief or lengthy. I'm open minded.