I haven't seen a lot of harem anime, but it's not accurate to call all harem leads jerks. Keitaro from Love Hina, for example, isn't a jerk, he just has the worst luck and gets into misunderstandings all the time.
Yuichi (Kanon) and Okazaki (CLANNAD) aren't that much of jerks either, at least, not in the way of "Oh, I'm gonna try to find a way to get all of these girls at once." (I don't know about AIR, but it's likely the same.)
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