Aren't all the red flags people are talking part of the natural dating process? You meet people, you have a great time together, but over a longer period of time, things come out that you don't like so much. Nothing particularly wrong about it - the person is just not for you. So you break up.
I wouldn't necessarily hate ex's because they did silly/stupid things that you can't agree with. Ever think that they have the same view of you? - being in a relationship sometimes makes people act irrationally. Whatever happened, I would try to just take the view that they weren't suited for me and thats all there is to it. Time is a healer and I guess over time I look back with rose tinted glasses - forgetting the bad things and remembering the good things. Thats not a bad way to remember someone from a relationship in your past, rather than remembering all the bad things - life is too short for that.
I guess for every failed relationship, it helps make a clearer picture in your mind of what you do or don't want in a relationship - so in a sense, going through the mill with an ex can sometimes be a helpful thing long term.
That said, I suspect males/females look back differently over failed relationships. At least thats my impression from my male/female friends and my own experience.