Not a straw man; a reductio ad absurdum.

You said, quite clearly, "Parents have a real genetic investment in their children, which is why they form attachments to them." Ergo, if a child does not share your genes, you will not form an attachment to them. Thus adoptive parents will not form an attachment to their children. My argument follows *directly* from yours. It's not my fault that your argument (and your understanding of evolutionary psychology) turns out to be made of straw.