[nosse]

"Finally, by linking homosexuality and incest, the poster tries to create a link between homosexuality which is now acceptable by most people to incest which is universally unaccepted and immoral. In western countries one is also legal and the other isn't."

I agree with you, but this argumentation is quite terrible.

If your main argument is "homosexuality is now universally accepted and normal". Then punishments to gays before being gay was accepted and normal are completely justifiable. Like Alan Turing's hormone treatment was ok?

Legality is just a approximation of this "is now universally accepted and normal". So it's weaker argument than the previous.

If you accept homosexuality because "no harm done to anyone". Then you should logically accept all other sexual stances as long as no harm is done to anyone. Right?