LA /San Fran

Bonhomie

Don't let it put you off. We did it as part of a road trip. Nowhere we went felt dangerous or even uncomfortable. As we were on a road trip, we might go to random motels. Some we decided...no way, as they looked like local housing But we found suitable places along the way. You do get some characters. We had 'producers' and 'actors' at ours in Wilshire Boulevard.
 

SW17

Homelessness is an issue in all major US cities, just as it is in UK and European cities. It's the real world and you will see it in California, not just in LA and San Francisco. The vast majority of them won't bother you at all. There is an increasing issue with opioid abuse (Fentanyl etc), and the poor souls affected by this are in a world of their own.

LA is quite spread out, and so is the homeless population. If you're in areas like Hollywood, Santa Monica etc, you'll see them but unlikely to be bothered by them. I saw quite a few homeless people in Beverly Hills when there recently. The most dangerous areas of LA aren't dangerous because of homelessness, and that has been the situation for decades, tourists aren't likely to be in these areas. I love LA, but it is a bit marmite.

In San Francisco, the greatest concentration of homeless people is in the Tenderloin area, which starts a couple of blocks to the west of Union Square, roughly south of Geary. It's not particularly dangerous, at least in daylight, but you will see some sad and occasionally unpleasant sights, Some people less accustomed to big urban environments may be more likely to be shocked by what they see. From a tourist perspective there isn’t much reason to be in Tenderloin, but you might be nearby. There are homeless people in other parts of SF, but not in the same concentration.

None of this would stop me visiting either city, and I've been to both in the last year (LA multiple times), along with several other California towns and cities. The coastal drive between LA and SF is great, and it's worth doing at least a couple of overnight stops along the way. Do be aware that parts of the coastal road do get closed occasionally, as a result or either landslides or forest fires, so you may have the occasional diversion (currently closed in the Big Sur area south of Monterey and Carmel). I would heartily endorse doing the trip.