People suffering from autism struggle with a concept called 'theory of mind'
Neurotypical people intuit from a very young age that other people are sapient agents with minds that produce thoughts different from their own, and have access to information you don't necessarily have. A person with theory of mind understands that somebody up in a tree sees farther than you see on the ground, and may see something that you don't see, which they can then tell you about, thus sharing information.
Autism stunts the development of this faculty, and as a result autists have a pathological tendency to presume that everybody else thinks the way they do, experiences the things they experience and comes to the same conclusion they do. It's intuitive to an autistic person that any opinion they have (eg. ORANGE WOMAN BAD) isn't an opinion at all, but rather a fact, a consensus held by every other interested party.
Autists use "we" when they mean "I", because to them there is no distinction. That inability to recognize and accept that other minds but their own exists is the source of most of their shitposting. Misusing "we" to imply a consensus among anonymous posts is a dead giveaway that somebody either has genuine autism or is simply a bad-faith actor coopting the distinct diction of a local thread autist to stir the pot.