one of the classic arguments made by pro-choice advocates is the analogy to involuntary linkage. Imagine that you had woken up one day and found yourself linked to another person. You can free yourself, but then this person will die. You can also wait a year when you'll both be freed. Very, very few people will say that you have an actual moral obligation to continue being linked to this person, and this argument has been used time and time again in the context of rape-related abortions. I am politically pro-choice and would not dream of trying to argue that in such a case you would be legally obligated to maintain the life of another person. On the other hand, i will absolutely judge, on a personal level, a person who just said "screw it, i really don't care" and unlinked himself.
In the case of the murder of kitty genovese (for people who don't know this, this woman was stabbed and basically screamed for like an hour while people just ignored her and eventually died), the bystanders didn't have a legal obligation to personally make sure she got the medical help she needed. Indeed, lots of people, maybe even most, who wouldn't have helped her for fear that somehow they would get in trouble. Does it make it okay that they just watched her die? F*ck no. Yes, it's "understandable", just like how it's sort of "understandable" that a kid who was sexually abused by his dad would become screwed up and a serial killer one day. "understandable" does not equate "moral".
Tl;dr: Just because something is legal and your choice, doesn't mean it's ok to do it. It's totally legal and your choice to watch someone die before your eyes and not call for help, as long as it's not yours. But if you do it, i will judge you and consider you a person of inferior moral standards.