Okay so I'm going to try and ignore the OP's use of the word "crime" and the general nature of the post since it's...just so meh.

Sex in general is looked at by many in a harsh light mainly due to left over puritanical ideals. Especially in America. We are the land of the free with no set religion yet far too many of the things about this country are religiously based. I would imagine masturbation can be viewed negatively because it's sexual, and it's enjoyable and from what I know most classical religions want people to view sex as some sacred act.

Granted, some people just do not like masturbation. It's odd since yesterday this was a topic in a Skype call...one person just doesn't masturbate, never has and has no interest in it. They don't care if others do it but they just don't want to themselves. I'm not sure why, I think their view of intimacy and affection in general is skewed for whatever reason but perhaps it's just something they need to grow into, or maybe they're asexual. But they're still a good person and they have their own personal likes and dislikes.

Aside from religion I think a lot of times people are raised in homes were sex never comes up. It isn't talked about, it isn't addressed and parents just assume they'll know when to bring it up to their kid or never will, or the school will do it. Kids begin to notice their bodies and the body's urges young and without any guidance they can easily begin to feel shame and then associate sex or sexual acts with shame.