Where has anyone allowed homosexuals to adopt for the purpose of studying the effect on kids?
It's been pointed out to you numerous times that studies on this issue are necessarily imperfect. It's not something that can be done in a controlled and observable environment.
No one is attacking the researcher. He apparently has an agenda and we do not have their data. In any court, the bias of witnesses are open to question. Bias can certainly distort research. For this reason, until the results can be reviewed and replicated, no one study can be conclusive, especially not one where the researcher has a pretty clear bias.
So, you don't have any verifiable proof for your claim. In essence, all you have is someone else making the same claim.