I do see a lot of them being banned
Is it cheating to accept open challenges from players with very high ratings?

I also will accept open challenges of players much higher rated than me, and when I beat them they will accuse me of cheating. For instance, a few months ago I nearly beat a 2000-rated player in blitz, and he only won because of a time scramble. He said that proves I was cheating, because in the time scramble I didn't have enough time to check the computer's moves; I defended myself many times, saying that I wasn't a cheater, but then just gave up (obviously, I wasn't cheating because my accuracy was 79%, and his was something like 68%). He said he reported me, but I just ignored him and went to find a new game with a higher rated opponent.
I think what happens is that these high-rated people aren't expecting you to actually be able to beat them, so then when you do beat them, they get very upset. I would just ignore what they say. If you cheated, you'll get banned. If you were playing fairly, they'll see that you didn't get banned and hopefully then they will believe you.
Is it cheating to accept open challenges from players with very high ratings? I'm asking because I do that a lot and they end up losing at least 16 rating points. Then the player I beat banns me and probably reports me because he thinks I am cheating. For example, yesterday I beat someone in bullet by checkmate whose rating was 1650. Then he banned me and probably reported me too.