Where are you getting the perception that Americans generally fear London?

I don't know a single American that has ever expressed any sentiment that London is unsafe. I know a few that have some stupid notions about immigrants in the UK, but that isn't exclusive to people on this side of the pond.

Genuinely, though. Americans just don't worry about safety in London outside of scams and petty crime inherent to any big tourist city.

I wouldn't say it's a general belief, but it is a point that certain groups like to push. See e.g. https://www.economist.com/leaders/2026/01/28/haters-on-the-r... (paywalled, but even the first paragraph is enough).