Kodomo no jikan is a deep story that is just too culturally difficult for mainstream westerners to feel not-icky about experiencing because it deals with sexuality and the protagonist is a child. It's actually a very sweet coming of age story and it doesn't hold back punches about anything (the mangaka is a woman with daughters in fact so she writes from experience) but all it takes is some random moment of sex-related stuff and people will brand this as shallow fanservice for weirdos and stop paying attention to the actual story, thinking it's just used as an excuse to show suggestive images.
But yeah people just see one masturbation scene and the alarms go off in their head and they never touch the thing with a ten foot pole. Fact of the matter is, for every sex-related plot there's like 4 dealing with things like getting your first period and learning how to wear a bra and dealing with the loss of a parent and stuff like that.
Oh and the humor, god the humor. The vast majority of the sex stuff is actually gags. It's a really funny manga on top of having great char development.
