I don't see how it's stealing.. You (as a web developer) don't have the power to require me to display any part of your HTML. Would it still be wrong to disable stylesheets on an obnoxiously coded page? I realize it's a bit different since ads (in theory) make money, but the principle is the same.
The thing is, the bit of difference is actually quite a big difference. It's the difference of helping yourself by not hurting others and helping yourself by hurting someone else.
It's the difference between reading a newspaper you found on the street and reading it over a stranger's shoulder.
It's the difference between adding a few pieces during a game of chess against yourself and doing the same against someone else.
It's the difference between walking down a street and pushing someone aside to do that.
It's the difference between reading a book in the library and reading it in the bookstore.
