You don't care about death threats until they're directed at you, your family, or the pets you love. If you're being dogpiled by extremists, there's a very real possibility that it'll escalate to doxing, swatting, and/or actual attempts. This happens frequently on twitter, even with its attempts at moderation, but it would be considerably worse with no moderation.
People making life-sized dolls of you, then filming themselves shooting it in the head and posting the video is legal. Them doing sexual acts to the doll, saying they're practicing for when they break into your house, filming it and posting the video is legal.
A lot of things that are absolutely terrifying are fully legal. Sites don't allow them because having subsets of users scare away other subsets of users is bad for business. If you have to pick between one set of users and another, usually the one posting hateful, threatening content are the ones to (rightfully) go.
i weirdly dont care about hypothetical death threats as much.