Imagine, a couple of San Francisco residents responding to a question about San Francisco in a San Francisco thread?!
The guy didn't ask what he'd see in San Francisco, he asked if it was dangerous as Fox news portrays. No it's not. Its one of the safest cities in the country actually.
You will likely see some fucked up shit, especially in the touristy areas. Desperate people live desperate lives, and tourist usually have money and downtown offers access to services. That said, they are rarely a threat other than maybe asking for money - I usually try and treat them as human beings by looking them in the eye and either saying no, I don't have anything or maybe offering some change if I have it. Sometimes they'll do something extra wacky for attention and shock value. Maybe there would be less of them shitting on the street if we offered them someplace else to shit.
I was in New York last year. Right in Manhattan, waiting on a train with friends who live there when some crazy dude straight up body checked and posted up on me. Most threatened I've felt in years. Luckily the train pulled up and we boarded without further escalation. Joked on the ride about my "real New York experience. You don's see me on the New York threads telling people how unsafe New York is based on my personal antidote as a tourist.