Hard to judge an international city using only American standards.
Homicides per 100k (from a couple of years ago):
San Francisco: 4.5
US: 6.3
UK/France/Germany: 0.8-1.2
Living in the Mission there are a handful of shootings per year. But it's a pretty dense neighbourhood so per population it's probably pretty normal for the US. The level of street homelessness is shocking but not as bad as downtown and you get used to that after a while too. Petty crime is definitely a problem.
Personally I worry more about being hit by a car crossing the road since cars are allowed to drive through the pedestrian crossing even when there is a walk signal.
Is there a racism issue or is it that ethnicity based gangs exist?
I generally feel significantly safer in cities with relatively walkable sidewalks, relatively narrow streets, and lots of pedestrian/bike traffic than I do in typical American suburbs full of strip malls and 6-lane roads. The latter are in my opinion horrendous places to raise children.
note, I also live in the Mission District and it's a shit hole to me. Gangs hanging out at 20th and Mission fronting for each other. Illegal markets all up and down the street selling stolen goods. Traffic signs and laws being ignored. Valdalism everywhere. Homeless under my window. Mentally ill screaming at 3 am. People drag racing at 2am
school allocation is not based on location in SF
Most parents who need to drive their kids across the city are doing it because the alternative (their kid goes to the nearest school) is, in some way, worse.
We lived in those neighborhoods cuz they were cheap and there were community services to fall back on. Once our parents could afford it, they would move out as soon as they could.
Gorehs/Gweilo are weird.
It blows my mind that people are so uncaring about their kids' daily experience (mobility, independence, access to interesting activities, ...) as to move to typical American suburbs with their kids. The benefit of the suburbs is a bigger amount of personal space at home for the same price, but everything outside the house kind of sucks, especially for kids.
We're not necessarily the "techie family" you are imagining though; I spent about a quarter of my childhood in a medium-poor city in Mexico, and my wife grew up in China. Personally I really appreciate having a quite diverse cast of neighbors.