You don't need a penis to excrete toxins. Had you had a nasty accident during circumcision, you would almost certainly be able to pee, albeit sitting down. But, without modern medical interention, you would not be able to reproduce.
You can, of course, facilitiate the propagation of your genes in other ways besides sexual reproduction, albeit far less efficiently. But, getting back to the original point, the human penis certainly has two functions. I don't see why we're wasting our time with this obvious point.
I didn't argue against that. I merely stated that one function, the excretion function, was essential for survival, and I threw in the sphincter reference as an illustration.
Because some people resort to red herrings when they sense that their points are being successfully deflated.