Men who already piss everywhere aren't too worried about a little splashback.
Ok, nice generalization.
You're ignoring some key points; this has been tried in Germany (this is where San Francisco got the idea) and it seems to be completely successful. And as a man who lives in SF neither me, nor anyone I know, has ever peed on a wall in a public place in the city to the best of my knowledge. The behaviour is really relegated to the homeless, whom I have seen doing this. For all the talk about piling on the poor homeless they really don't appear to give two f*cks about other people. There is a huge problem in San Jose, which is at the other end of Silicon Valley where homeless encampments sprout up, and wherever they do they create a huge trash/fire problem. The police come and shut them down, and they sprout up elsewhere. It would be one thing if they set up and were respectful of the environment and other people, but they never are; drugs and crime (rape) are the order of the day in these encampments.
Lastly, we need to do something. A friend of mine was here last year during the summer and his remark was "Beautiful city, too bad it smells like pee." Could have been the bay, or maybe it was the pee. Either way, it would be nice to not have people peeing like animals all over the place.