Assertions made without evidence can be disregarded without evidence, and your assertion does not match my personal experience. Public transit is dangerous, especially in cities like SF or Seattle.
It’s a safe bet that sndgndgndgndy isn’t referring to that metric, but to the (perceived) probability of getting shouted at, mugged, etc.
That, I have been told, is definitely a problem in the USA. I think that’s because they’ve painted themselves into a car-centric corner that it is very hard to get out of.
Outside of a handful of American cities, public transit is mostly used by the poor, which can include a lot of "undesirables", and many people used to their "quiet, safe" suburbs feel deeply uncomfortable around the poor in general. In some cities, public transit is used as a du-facto shelter system by the homeless.
It's funny when people see celebrities use the subway in NYC. It's just accepted by New Yorkers that the subway is usually the best way to get around Manhattan and getting mixed in with the entire socioeconomic spectrum is normal. But the crowds of people is also a kind of security blanket if something does happen.