That's a good point. Although I think it would have been more interesting if he'd had to kill Leia instead, since she's the one with the Jedi bloodline. And it would have been a nice twist to bring in the mother/son relationship as opposed to the father/son relationship.
As an adult, I find it hard to buy that Kylo Ren has chosen the dark side because of his grandfather. It's like, doesn't he know that Luke saved Darth from the dark side at the end of the original series? You'd think that would be a pretty big part of the family history to pass down. Lol! However, I'm far from an expert on the subject so could very well be missing something.