My take was that most people 1) don't want Meta/Facebook spam - low effort memes, propaganda, etc. and 2) don't want their content to be used by Meta. The former seems pretty easy - just defederate and you don't see any of their crap. The second is sort of a gray area... Whether or not you are diametrically opposed to Meta/Facebook or not, once you post your content to a public site, it's available. I haven't been here long, but defederation seems to work both ways, so FB would have to scrape content from known instances to get that content unless I'm mistaken.

FB could smoke any instance by DDOSing scrapes whether intended or otherwise, but once you post your data on a public forum, Meta could theoretically use it.

But to your comment - I don't see what starting a new instance would do for anyone for #2. Any new instance is discoverable by nature, so FB can come knocking at any time for content whether you defederate or not.