I love it when my favorites win, but I like seeing them get the crap beat out of them too. It makes their eventually victory that much sweeter. And it reminds us that what they're doing is actually terribly dangerous.
I like seeing Superman beaten up on occasion because I think it's important to remind people that yeah, he's bulletproof, but the stuff he fights on a daily basis is every bit as capable of hurting/killing him as the people Batman or Spider-Man fight. Superman doesn't seem so boring and invincible when he's got a black eye and fractured arm. And when he keeps going after a beat down? It just reminds us that powers or no powers, he's one stubborn tough SoB.
As long as the character is respected, I'm more than fine with seeing them defeated, either physically, mentally, or otherwise. Failure is how we define character, after all.
Now, I'm not interested in seeing my favorite characters get sh*t on by writers trying to elevate someone/thing else (don't red shirt my favorite C-listers!), but an honest loss? That's great, actually.