At the time of Wonder Woman's creation, the notion of a woman exposing her legs would have been a defiant and progressive statement. There is no modern equivalent, but pants are a lot closer than having her show skin for the sake of teenage boys wet dreams. They would also be more practical.
I was fine with the Jim Lee redesign, though I would have liked it more if there were any possibility that she could ever button the jacket over her massive boobs. (And no, I'm not calling for a larger jacket.)
The TV costume is simply awful, and it has nothing to do with the pants - it's just bad.