Many Christians simply haven't believed the simple statements of Scripture like Romans 5, 1Corinthians 15, and 2Corinthians 5 where we're assured that Jesus Christ is the total undoing of all of the evils that came into the world through Adam's disobedience to God. Those Scriptures assure us that He's the justification of life. That's a strong statement that can't really be backed up with ideas of exclusivity being taken to Unbiblical extremes. Yes, sanctification is important, as well as maintaining a pattern of sound Words from the Gospel, etc., etc. but the only exclusivity about the Gospel is that no one comes to the Father except through Jesus Christ. He's not looking to keep anybody out! But He's the Door.
He's there right at the moment of their death with their life review during which they find out where they missed it, Who He is, what He's done for them, and they go with Him and not to the devil. Of the 4 words that get mistranslated as "Hell" in the KJV, I've yet to find where a single one of them necessitates afterlife punishments:
Sheol in the Old Testament and Hades in the New Testament are simply the grave. Our worst critics will give on that one, even if they personally believe (based on no Scriptures in particular) that it means more than that.
Tartarus in the New Testament; along with the fire prepared for the devil, his angels, and the goats in Matthew 25; the fires of 1Corinthians 5; and the Lake of Fire are all judgments of our works. Yes, there can be suffering involved with this. We all go through that when we did what we thought was a good idea rather than what was the God idea for our lives.
Gehenna, which is the word that Jesus used the most that people mistranslate as "Hell" is used both in the synoptic Gospels and in James and it's simply the consequences of bad teaching or a wrong paradigm. This one, according to St. James, sets on fire the wheel of the course of nature and can really get us into some of the deeper evils of life because our heads aren't screwed on straight about this or that, or perhaps about everything.
A lot of people will try to say that the Biblical Universalist doesn't believe in consequences for our actions. We simply believe in just consequences and the different levels of sins and punishments that the Bible speaks of when it gives Old Testament Israel as our example of all of these things. Things not forgiven in this age or in that which is to come simply run their course in the individual's life and then have consequences for following generations. Jesus' comment along those lines was the New Testament equivalent of the Old Testament "the sins being passed down to the third and fourth generation." But as He promised to restore Israel to their land, to restore a Biblical language and faith to them, and to reveal His Son to them throughout the Old Testament, we can likewise be assured that He'll deal as graciously with every nation, city, and family that's ever existed based upon identical promises in the Bible regarding each of them. All of the promises of both destruction and restoration will be fulfilled, so that you've got even the salvation of Sodom and Gomorrah in Ezekiel 16:53-55. And the KJV in Jude's epistle calls them "the example of eternal fire."
There's not a verse in the entire Bible that teaches the perpetual damnation of a single life anywhere.