Some couples enjoy it. That is not a myth.
Why does anyone else care if they do?
Why does anyone care? Well perhaps because it affects society at large.
It will spread more STD's, which we will all have to pay for, it will create more unwanted children or abortions, which we will all wind up paying for, it will cause more broken relationships, which again filters down to harming children, and we have to splain and try to convince our children that this is wrong and that they should not embrace it, even though more and more in society seems to be doing so.