The kid my partner and I raised could attest to that. We fostered him as an alternative to institutionalization, after he'd all been written off by the system as too damaged to be placed after years of abuse and neglect.
He thrived with us, and he didn't stop being straight just because he had two gay dads.
Our little gay family wasn't so different from many. Gay people are highly likely to adopt or foster, and we're more likely to shelter children who are hard to place.
I have to ask myself how anyone could consider that harmful to society. I think the basic problem is that people often just don't consider very deeply.
Decades ago, before same-sex marriage was possible, my husband passed away after a long illness. We were registered domestic partners, which was all that was possible then. But even so, I was not legally able to inherit our co-op apartment, my home for 10 years.
The co-op agreement specified that only legal spouses and other specified close relatives could inherit, so I was out in the cold.
I'd still be living there if we'd been allowed to marry.
I wonder if people think about things like that when they object the same sex marriage.