[Is it abuse to be a male in RL playing a female avatar in SL?]

Yep, me too.  I think I look just fine so my ava looks as much like me as possible.

[Is it abuse to be a male in RL playing a female avatar in SL?]

The answer is..it depends.  Depnds on how far the representation goes and what actions are being taken based on it.  I know some ava's who say in their profile or otherwise tell--always ok.  But I know some others who have also represented themselves as the opposite gender in RL as well, even using a voice pitcher to attempt to complete the illusion and using someone else's photos.  Not cool.

Bottom line, we all have a basic right to chose who are sexual or otherwise intimate with.  For some people, the gender of the other ava is a deal maker/breaker.  Right or wrong, there it is. Some ppl can be hurt or even traumatize by a deep deception.  I've seen it happen--more than once.

Many ppl want to simply point to the TOS and give a quick and decisive "nope" as an answer.  No so fast please.  Avatar's rely on humans to exist--not considering bots.  Those humans have real feelings so, like it or not, there are some ethical obligations here (and perhaps some legal ones).

My two cents, I don't care about your kink--as long as you obtain consent honestly from one legally capable of giving it.  If you have that, have fun! 

For those of you for whom RL gender is a deal breaker, remember one of the cardinal rules of SL:

NO VOICE, NO CAM, NO CHANCE.