From a infertility perspective I think alot of infertile couples are hesitant to resort to adoption until they've exhausted all other options because they're holding onto having a child that's biologically theirs. Fertility treatments for the most part are financially way less than the cost of adoption, atleast in Canada were im from. Infertility brings alot of unsolicited advise like "just adopt" because I believe people want to help and offer a solution to the problem and adoption is a sure shot way of having a child. I've never heard any concerns about overpopulation except coming from people giving reasons they're childfree.

I think everyone who has it in their heart to open the doors to parenting through adoption or fostering etc should.