Did everyone in that comment section forgot the part where she said "my adoptive parents refused to let me see my biological parents"?

This act is selfish. You cannot deny an adopted child their own biological parents. Essentially it is NOT UP TO YOU to decided if the child can see them or not. The best thing you could have done is to tell OOP that they will wait until for OOP is older to discuss that issue. But to outright refused OOP the right to meet with the reason of "you might prefer them more than me" is petty.

You adopted a child. You have to come to term with the reality that you are not in a situation where you can pretend everything is going to be normal if the child wanted to know where they came from. As an adoptive parents, you sign up for this. And if you broke the child's trust, that was on you.