I wouldn’t say it’s “wrong,” but I’m not entirely sure that it’s the right thing to do either. By their marriage, the couple is creating a family, which naturally means that they should ordinarily be focused on having children of their own. To marry in order to intentionally adopt unwanted children to the exclusion of having children of one’s own – as distinguished from a couple who adopts when unable to have their own children or who adopts in addition to having their own children – seems almost like the couple is starting an orphanage rather than a family.