Peter doing it with a prostitute and selling drugs to kids wouldn't happen because we know Peter. We know his past, and we can see him internalize everything he does before he actually does it.
With Gwen, we never had that luxury. Gwen was wholesome and good, but we never got to really look into her heart the way we look into Peter's If we could, then we may have seen that she was really longing for Peter, and seeing as how Peter was mister shy back in the day, then maybe she found something in the arms of another man that Peter just wasn't giving her. Should it have been in the arms of Norman freakin' Osbourne? HELL NO!!
Still, we can't undo it, and neither could Gwen. Good people do bad things. Peter once let a criminal run by and get away when he could easily have stopped him. How did that turn out? Doe sthat make Peter a bad person? No. He made a mistake, and he learned from it. Gwen made a mistake, and she learned from it as well. She tried to make things right with Peter, and she was wanting to tell him the truth. She also alienated Norman Osbourne to protect her young children.
Now, had Gwen gotten knocked up by Norman, and then ran off and started ****ing herself out on Hollywood boulevard so that she could afford an abortion, then I could understand everyone being a irate about it. But, that wasn't Gwen. She was a good, caring person, and she loved her children, no matter who was the father. So, she did the best she cold, and, had she lived, may have ended up raising them with Peter and even having some more children down the road with him.
Things just ended up the way they did. It happens.
As far as my approval of the story, JMS hasn't won that yet, but he still has a chance to win me over. A slim chance, but a chance nonetheless.