I haven't read the legislation in detail but I don't think it makes gay marriage compulsory for everybody.
As far as evolution goes sex is very variable. The majority of living things don't do sex at all, many practice bi-sexuality, some can switch from asexual to sexual reproduction depending on resources, some are hermaphrodite, there is a marine flatworm that fights duels to decide who gets to be the male and there is a fungi that has not 2 sexes but 28 000 of them. Apparently number 27 999 is widely considered "unnatural".
Cofty thank you for making me laugh, it's been a crap few weeks.