I want to shoot a piece that I know will be very controversial and just wondering the legalities as far as expressing an opinion via art/photography. Anyone know?

shoot anything you want. for true art there are no rules of decency.

I suppose you can't harm someone or deface property in the process, however.

Here is a link that may answer your question. Really it seems to come down to wether or not it causes anyone or anything any harm or loss. If it offends or breaks a law (but doesn't cause harm) it still has to be seen as "artistic", otherwise, you could be prosecuted.
http://www.csulb.edu/~jvancamp/freedom1.html

They have recently added photography to protected acts, from my understanding. However, again, it must be seen as "artistic".

Janie,
Give us some details, so we can understand what you are looking for here.
Sounds like a fun project!
Brian

Wow - I think there are very few limits. From Lewis Hine to Weegee to Mapplethorpe to Nan Goldin and on and on - I'd say pretty much anything goes, as long as it's not blackmail. However, if you took two Barbie dolls and photgraphed them in questionable poses, I think Mattel might have some issues with it, so in a case like that, I would do some research on trademarks and the like beforehand. They've got fancy lawyers.

But like MTB Brian said, I can't really tell unless I've got more info. But don't limit your expression because you're afraid of what people think....

Megan