I think it's easy to blame the death of Halloween on being a "low-trust society" but I don't think that's it.

Even if you live in a low-trust society, you just take more precautions when interacting with your society members. The modern desire to shut yourself off from your neighbours entirely is NOT due to "oh no, what if someone poisons my kids' candy?" and more of "ugh, I don't want to 40 micro-conversations with strangers--or god forbid, people I know--over the span of an evening".

Like... it's less safety-oriented neuroticism and more a mass psychogenic illness of introversion.