Sabre - you said paedophilia. That's a very controversial subject and if you want to make play based on it, you have to accept all connotations under that broad umbrella.
In my country, the age of consent is 16 years old. Sex with anyone under that age is considered statutory rape since the minor cannot give consent. This is assuming the older party is 18+ I believe.
I doubt a chicken, a goat, a cow or a dog is able to give consent for anything. Your argument here, like paedophilia, is moot.
Incest is a completely different thing altogether. To have healthy offspring and limit the chances of deformity it is neccessary to outlaw certain types of close related incest (although cousins can marry if I'm not mistaken).
The comparison between polygamy and gay marriage is as valid as the comparison between polygamy and heterosexual marriage. Adultery is between consenting adults and is not a criminal offence.
Tolerance and approval are different things. But not allowing gays to have the same legal rights as a heterosexual couple is not tolerance; that is active discrimination based on a value judgement.