A legitmate reason is that it's against God.
If you're not Christian, however, a good reason against it is that kids need to see a fatherly AND a motherly figure in their lives.
This is a subject that I really wanted to be brought up.... so if you think it is against god because it is in the bible... do you also hate people that aren't christian, I mean the first commandment IS you must believe in one god. So people that are not Christian are breaking that commandment.Correct? So if you will say gays are sinning you are also saying teenagers that argue with their parents, people that dont believe in god, ect. are also people to be disapproved of. It something to think about.
I don't hate anyone, only my own sins.
It's not my place to judge tbh.
I do think though that you are right, children do need a motherly figure in their lives, but i dont think it has to be a mom. It can be anyone, an aunt, sister, friend, teacher,ect. Thank you for debating, some people dont and it can be very annoying and rude. It is nice hearing another side opinion and this IS debate.