Gee, it seems that Mr Shapiro is missing a couple of important points.
First, there is a very pertinent reason to disallow incestual marriages: They are likely to produce mentally challenged offspring. This is very unfair to the child. This is not the case with a gay couple seeking marriage.
Second, there are no incestuous couple clammering for marriage rights. I am not aware of even a single couple coming forward and requesting the right to marry. Mr Shapiro is trying to make us fear a problem which does not exist.
Third, just because you make a movie about a bank robber, doesn't mean you are advocating or championing bank robbery, does it?