The media, like the characters in Four Seasons, are very forgiving of happy couples that met though infidelity.
Celebs are role models, like it or not. We don't act any better than our role models, do we?
What did Brad see in Angelina? Someone wild, romantic, passionate, free with her emotions, maternal and interested in changing the world.
Jennifer was glamorous and beautiful, but it seemed, a little less deep, more restrained and, "sterile".
Brad and Jennifer didn't have children (not that this seems to stop people these days)so there was less holding them together. There were no financial obstacles (both had tons of money). What negative consequences would follow? So why not leave your spouse and follow your bliss? Brad saw no obstacles to geting what what Roger Ebert calls "the prospect or perfect personal happiness."
The right thing would have been to stay with his wife (given my religious understanding). The passionate, "joyful" thing was to go after Angelina.
There's a great article by Larry Crabb about this very subject from a Christian perspective. He says that we, as Christians, expect that by doing the "right thing" we will, in most instances, be more happy. What if there was someone (OW/OM) who God does not intend for you to be invovled with who could provide perfect, personal happiness? (Or at least more happiness that you have known in your current marriage, family or career)? If it's all about being personally happy in this life, without the prospect of the Life to Come, then how could we fault Brad?