The untutored or perhaps commonsense view is that there’s something out of order about certain sexual acts. They’re “unnatural,” as people once said, or “intrinsically disordered,” as the Church says today.
Nowadays of course educated people think that’s all ridiculous. After all, no one says sodomy or whatnot is miraculous, so it evidently complies with the order of nature. And all intentional actions are unnatural in some sense, since they change what would happen if we let things go their own way.