George Bailey was actually quite the putz. Not that Sam was better, so Mary got herself caught up with two bad men. Back to George, meanwhile: in the beginning of the movie, he verbally abuses her and talks about having a harem when he grows up. In the scene in which he goes to the high-school dance, he sexually harasses her—and there is nothing cute or funny about taking a robe from a girl and claiming that everybody will be on your side for your doing it. In the phone call in which he goes to her house, he gets physically violent with her during the phone call with Sam—and he had already gone there uninvited and became verbally abusive toward her when she asked what he wanted.
Clearly by now, there is a progression here that should be seen by and to troubling everybody whom watches the movie: George Bailey was a verbally-abusive and misogynistic young boy, and he never grew out of that when he became a man. In fact, it got worse as he became older. He may have had moments where he seemed like a nice guy, although he ultimately wasn’t— and if it wasn’t already reflected in how he treated Mary before, it was certainly reflected in the way that he took the phone from her when Mrs. Welsh called, verbally berated Mrs. Welsh, and then proceeded to verbally abuse his family as well as violently break multiple objects in front of them.
He also mistreated other people, including his mother, Annie, and his uncle Billy. So, Mary was not the only victim of his could-be-charming-and-was-ultimately-a-toxic-person self.
PS On Reddit, where I originally posted this, I already received one verbally abusive comment and have seen other comments in which the posters are defending George Bailey‘s behavior just because he did some purportedly-good things (notwithstanding what his motives might’ve been) and/or took up causes which they support. They’re only going to prove my point as well as making me wonder who they themselves are abusing.