Imagine someone running up to someone with epilepsy in public and showing them strobes? What sort of deranged person does that?
Imagine someone sending death threats through snail mail over and over. Of course that's horrific! But brigaders doing it through twitter is kinda fine because "hey, you're on twitter, stupid stuff happens".
So much harassement is extremely cruel but we (myself included) tend to discount it when it happens over social media.