Why is Hank Pym persecuted and irredeemable when Peter Parker beat a pregnant MJ...

and got away with it? Or when wolverine would slap around Jean Grey. Why is it hank pym is permanently tainted when other characters have done the same or worse?

Because, along with creating Ultron, it is the most memorable thing he had ever done, and unlike the Spiderman example, it's in a story actually worth reading.

It could be because his has and inferiority and persecution complex. So he can never get over it and always has to bring it up.

Spider-Man slapped MJ while he was fighting Ben Reilly, his intention wasn't to strike her. Still a horrible moment in Spider-Man history, though. No excuses.

It was an accident.

Peter Parker hit a pregnant MJ and knocked her across the room hard enough to damage the wall.

But Spider-Man is not the only superhero to have done despicable things. Reed Richards has punched Sue Richards and Franklin more times than Rhonda Rousey did her last opponent.

Iron-Man has killed Avengers like Rita DeMaria, locked Avengers in prison for not revealing their identity, hit women, tortured children, and even had underage Mutants get naked with him to fight (ewww!!!). And yet, he too is not labeled like Pym is.

Why is Pym forever labeled a "wife-beater", when others who have done far more heinous things are not seemingly held accountable for their bad behavior? I believe it is because a) there isn't a lot of other history with Pym - for the most part he was a background character with little character development, b) The story was widely known and distributed and c) writers have not let it go. Pym's character ever since then has been one of redemption. Whereas no one brings up Spider-Man's punching his pregnant wife, Reed's punch fest with his family or Iron-Man's killing spree, or his torturing kids, or his naked romps with underage X-Men. Most every story with Pym mentions the slap at some point or his creation of Ultron.

Another reason no one brings up Spider-Man's denting a wall with his pregnant wife is because it would damage comic book sales if it became too widely known.

Spiderman and Wolverine are likable and have fans; Pym not so much. In all honestly Pyms thing is blown way out of proportion, unless you're talking ultimate and no one should do that.

Life isn’t fair, some things stick and some things don’t. In fiction and in real life that’s just how it is.

To be fair the same can be said for Pym. Jim Shooter explained the instance here. I think the real reason is Pym has no other notable stories in his history aside from creating Ultron.