the thing is, you really don't even need to look at #Facebook's past to know blocking Threads is an absolute must. there are literally organisations calling for the murder of queer people with accounts on #Threads RIGHT NOW.
any instance that commits to "active moderation against racism, sexism, homophobia and transphobia" (which includes all the instances in https://joinmastodon.org/servers , by the way) is in violation of their own ToS if they DON'T block Threads.