I have a sense that the islands (instances) are concentrating/amplifying more extreme views echo chamber style. I'm sure it was there on reddit too... but I feel like I am exposed to more far right and far left viewpoints that are presented in a toxic/offensive manner on lemmy. It happened occasionally on Reddit but it is daily on lemmy. I am browsing All to find new content and not really liking what I find.
I haven't seen much far right stuff here, but I see toxic far left rhetoric all the time on Lemmy and it's honestly extremely off-putting even as someone who's solidly ledt if center.
Yeah, I think it is a consequence of the nature of federation like you said (not saying federation is bad, of course)
At Reddit, everyone had to coexist and conform to the overarching group of admins and site-wide policies, whereas anyone on Lemmy, should they find the admins of an instance too restrictive, can just make a new instance that allows for whatever extreme they desire.
Thankfully, a lot of the major instances like lemmy.world seem to be closer to the middle- still biased one way or another, but not nearly to the extremes of Lemmygrad or Exploding Heads