Even 5 years ago I would. But the level of mayhem, filth, and danger on San Francisco public transit is out of control. The BART makes the Tube look like Tokyo Metro.
I’m not the poster, but personally I would.
I go to London quite regularly and usually stop by San Fran once a year (not 2020). I personally find the BART similar to the MARTA (Atlanta) and DART (Dallas).
I don’t know if you live in London, but I would say they compare to the Northern Line it terms of quality. But at the end of the day the real difference is about riders. I would say you do notice more issues like littering (including dangerous litter like needles) and robbery in the US train lines though.
However, just like most public train lines, you have to learn to mind your business, be aware and don’t lallygag. Also, stick to using it during the day.