What if you knew a gay couple that wanted a baby? What would you suggest to them?
Assuming you're talking about two gay men (because it's far easier for two women to have a baby, the male part in the process being fairly perfunctory) I would suggest to them that they should make their peace with the fact that two males can't have a baby without the involvement of at least one woman, probably two - one to provide the egg, one to gestate the baby. I'd also talk them through what's involved in both those processes, in detail, and point out the risks they are asking these women to undertake on their behalf. Then I'd explain that's why I believe it's unethical for anybody, whatever their sexuality, to 'use' a surrogate to carry a baby for them. I see it as a form of buying a baby, and I believe that's wrong. It's not good for the baby and the baby's needs should come first.
Becoming a parent is a great privilege. Not everybody gets to do it. Plenty of people have problems with fertility, don't meet the right person at the right time, can't have a child for health reasons, don't pass the (rightly) very rigorous screening to become adoptive parents - or look into adoption and make a realistic decision that it's not for them.
There's no escaping biology. I think it's entirely right and proper that gay men should be considered for adoption on equal terms with everyone else. However, having a child to whom one of the men has a biological tie is a different ball game.
If all else fails, I'd ask why human babies are treated so much worse than pedigree puppies or kittens, who can't be removed from their mother for several weeks after birth.