The chances of you becoming an actual victim of gun violence in the US are still very low. 10 or 100 times the UK level, but still very low in absolute terms. (I'm not pro-gun, quite the opposite, but the actual risk among 330 million is very small.)
The problem is more the systematised fear of it. I've seen videos of US college students who come to Europe and choose where to sit in the lecture theatre on the first day based on where they would dive to if someone came in and started shooting, and their European colleagues go "Are you nuts?". Holding active shooter drill for 5 year olds must be hugely psychologically damaging.
I see people are mentioning healthcare, but if you have good insurance and a few thousand per year to cover the deductibles (excess) and co-pays, American healthcare is great. It ranks poorly on world surveys mostly because so many people (still) don't have access to it.
Something that would put me off is that Americans have different ideas of friendship. You can think you are quite close to someone and then they move away, not even very far, and they don't talk to you again. Not because you had an "unfriending" incident, it's just they don't seem to make the effort. Of course, exceptions apply and we have dear long-term American friends, but there is a "transactional" aspect to many relationships with Americans, I find.