Craig Carter has a helpful post on what he thinks is the real problem of universalism. He writes:
I propose the thesis that the main theological problem with popular ideas of universalism is that they ultimately make our relationship to Christ something less than the most important issue we face in life...Is living a comparatively good life - for your day and age and society - and maybe a bit of moral heroism sprinkled in here and there enough for salvation? What happened to Rom. 1-3? What happened to "All have sinned and come short of the glory of God?" (Romans 3:23) Why did Jesus bother to come and die anyway?
Usually, when this problem becomes apparent to would-be universalists who don't want to lose their Evangelical audiences completely, the next step is to begin speculating on the possibility of hell being eventually emptied by the love of God drawing everyone to Himself.
What this does is to make life basically unserious: "Eat, drink and be merry for tomorrow we don't exactly die, we just move on to a stage in which it will make a lot more sense to be religious than it does in this life."
What universalism does for this life is a big problem but I think it is not the big problem. The big problem is what it does to the final judgment. So for example here is the document Mars Hill released to defend Rob Bell. They write:
What does Love Wins say about judgment?
In the book, it is stated that we experience judgment now for choices we make and there will be the final judgment to come. God cannot tolerate sin and injustice and will judge acts of injustice decisively. Rob addresses God’s judgment in Love Wins several times [See pages 37-39, 49-50, 89-90.] In Love Wins judgment is also viewed as self-induced. When we continue to reject the way of Jesus we choose hell, bringing judgment on ourselves. [underline mine]
But a paragraph earlier they wrote:
What does Love Wins say about heaven and hell?
Love Wins recognizes heaven and hell to be realities all around us. We see hell everyday through the atrocities of war, famine, human trafficking, broken relationships, and abuse. We also see heaven all around us through acts of love, kindness, and compassion.
There is also the reality of heaven and hell in the future. Our ultimate future hope is a restored creation under Christ where God will dwell with us forever on a restored heaven and earth [Rev 21-22]. There are many who accept the invitation of the life of heaven and many who reject the invitation. Those who reject the invitation experience a purifying “fire” of judgment in hell, yet there is hope. We live in the hope that the redemptive work of Christ is beyond what we can ask or imagine. Love Wins helps us have a biblical imagination that leaves room for the hope of the redemption of all while recognizing humanities free will to continue to reject God.
So, we have final judgment but it really isn't all that final. Rob Bell tells us that because heaven has no gates people can come in from hell when they want. Gregory MacDonald writes, "The universalist would see the lake of fire as deserved and terrible but as educative, being aimed at producing a realization of one's sins and thus repentance" (The Evangelical Universalist, p.121). Thomas Talbott writes, "On the other hand, for those who refuse to step into his ordained system of repentance, forgiveness, and personal sacrifice, he [God] has an alternative strategy: In their estrangement from God, they will experience his love as a consuming fire; that is, as wrath, as punishment, and, in the the end, as a means of correction. So in that sense, they will literally pay for their sin; and God will never--not in this age and not in the age to come--forgive (or set aside) the final payment they owe, which is voluntarily to step inside the ordained system of repentance, forgiveness, and personal sacrifice" (The Inescapable Love of God, p.106). But in this scheme even after the final judgment when the person finally chooses he's done "kicking against the goads" as it were, well then out you come.
It is ultimately man who has control over the final verdict. Sure God may give the verdict, but when we say "uncle"--ok then, you're done. The final verdict is not a verdict but an educational experience. While this of course makes this life somewhat trite more than that it demeans the character of what God does in judging in order to set the universe right and establish his universal reign. Instead of letting God be God, man will always get the last say on his terms and when he wants.
I think the pernicious problem with universalism is that the "Last Judgment" is not really all that final and last. God can, in this scheme, change and redo the judgment whenever he wants. When man decides he's done God will change the verdict and welcome someone back into heaven. It will hardly do to say that the verdict is final with an included condition because meeting the proviso still nulls the actual verdict of "guilty."
So if the judgment isn't really all that final then the resurrection doesn't then really furnish proof that he's fixed a day in which he will judge the world (Acts 17:30-31). I mean he may judge the world on a particular day--but hey, if you want to come along sometime after that and do something for reversing the verdict so be it. In the end the day may be a day, but it isn't all that fixed. Eschatology may be inaugurated but never really gets all that consummated since whenever you want the final verdict reversed just let God know. Then it makes a mockery of the notion that God will be 'justified his his words and prevail when he judges' (Romans 3:5).
While I agree with Craig Carter that universalism makes this life trite as the "day of salvation" that is "now", (and this is no small problem), I think the greater problem is how it universalism robs God of his glory in the final judgement. Just my thought.