Hmm, to say ex's are ex's for a reason makes it sound like all ex's should be considered assholes. I've always hated the idea of putting down and criticizing an ex just because a relationship is over, because then it makes me look like just as much of an asshole for being with that person, if they're supposedly so bad!
I've never had any relationships end because we were screaming and fighting, nor because the other person was crazy or mean or anything like that. In fact, I've mostly had really nice breakups, even if they were sad, where we just acknowledged that it's not working and wish each other the best. I always strove to be as mature as I could regarding ending a relationship. Then we can remain friends. The most painful breakup was my marriage ending, but I am sure we will be friends again someday. I think most of my relationships prior to my marriage ended because things sort of just fizzled out. Then a year or two or more later, we meet up again and hit it off. So, I guess that's why I never understood this concept of avoiding ex's at all costs, across the board, no matter what. I think, if it feels good and right, go for it!