It can depend on the different ways various people affect each individual. Take myself for example. It's easy for me to give Rumpelstiltskin a chance because as much as he has caused problems for the whole town before, he never did anything personally to me. So he and I have an understanding here. For as long as he doesn't do anything to hurt the people I care about, like you, your mom, Ruby, Belle, then I'm okay with him.
But Regina, I can't forgive her for everything she did to me. I know that probably makes me the bad person and I genuinely wish I could be one of those who could move on past these things, but I just can't. So I try to pretend she doesn't exist, as much as possible. it's better than giving into my hatred of her.