is it cruel to be kind to a masochist?

My understanding of masochism is that it is mostly a sex-related thing...i.e. people don't normally want to be masochists *all* the time. Also you're kind of talking about meta-masochism, and I doubt most masochists go to that level.

Then again I am neither a masochist nor a sadist myself, so it's entirely possible I may have no idea what I'm talking about.

Masochists gain pleasure from self-inflicted pain. I would say that people who automatically think that being a masochist is a bad thing are single-minded, because people usually think pleasure comes from eating candy or playing games, right? Some people don't gain pleasure from those things, and usually feel pleasure from pain. I would say that if that's how they feel good, you should respect their wishes. But for me, I feel bad for harming people, so i would just excuse myself and tell them that I don't feel comfortable doing it.

Ok. Unless you find yourself in a sexual encounter with one being kind is not being cruel, it wouldn't be anyway it would just be boring.

How can kindness be cruel. Your action is kindness, so that is all it is. Just because the receiver of your kindness is not kind, doesn't make you unkind.