"Isn't it more likely that a baby brought up by same sex parents would consider that to be the norm and may then regard heterosexual behaviour as abnormal" - Hmm no. I think that is a streach.

However I think a person brought up by a same sex couple would not view same sex couples as perfectly normal - assuming they were brought up in a happy and stable home.

As for the rights and wrongs of it all I'll leave that to others to be righteous about..