My problem with both universalism and Calvinism is that both (though especially the former) presume to know far too much about the hidden designs of Providence.
Maybe everyone will be saved. Maybe everyone will be damned. Maybe many will be saved or maybe very few indeed. God can do what he likes, and it isn’t really our business to know either way.
I should add that there is a similar but more generically Christian variety that bugs me - the people who assume that all those outside the Church and even all those they dislike within the Church are going to hell.
I freely admit though that this inclination on my part is a function of my more general distrust of system, rationalism, and explanation in religion.
This is also why I don't get terribly worked up when people have Universalism discourse. Who knows what's going to happen? All of this is mere speculation. Our own souls will be judged, and that is the chief point to keep in mind.
I'm basically a fideist, is what I'm saying.