It’s a bit true, and a bit misleading. Everything is down to perception and visibility.
Theft is absolutely not “legal” but it is true that police don’t investigate everything equally. Someone stealing shampoo from a store isn’t worth the cost of a police investigation, for example. More concretely, there was a recent policy from an old politician to essentially not focus on prosecuting “crimes of desperation” if they didn’t have a big impact (eg under $300). There’s some side affects to that, like increase in petty thefts, or the perception that they’re not being stopped.
I think there’s some unique issues like package theft that are probably pretty bad and probably structurally hard to solve. SF has a lot of townhomes and residential buildings that have a door on the street so stealing packages is probably easier than in suburbs or denser cities that have big building with mail rooms.
In SF, the homeless population is very concentrated (in soma, TL), and it makes many people feel unsafe. Statistics show it’s not particularly dangerous city at large, nor are you likely to be a victim, but that is cold comfort for someone walking alone at night, especially in these areas. I personally understand that sentiment and there are places I feel uncomfortable being, which is a pity. It sucks that someone well known and connected was killed, but it’s not really common and no one I know is particularly scared when outside on the street day to day.
I also think there’s a large cohort of people in SF for a job, but not because they like the city. I think that leads to being easily disenchanted and grumpy with the city. Especially when those people disproportionately move to the above mentioned sketchy areas (eg soma).
Also SF is literally known for being tolerant for generations. At one time, the hippies were just a local drug using homeless population here.