Where on earth did all these MN leavers crawl out from? Never seen before
a) when all you get is a routine barrage of insults, people tend to,stop posting. It doesn't mean people agree, it just means you've driven them to shut up. Brexit is not the only 'echo chamber' subject on MN
b) but, the worst of the Brexit insults are some time ago in the past, and there have been a lot of new members then. Who perhaps aren't worried about speaking up, because they aren't sick of the level of insults because they didn't see it happening.
c) and following on from b), I think the general tone of MN has changed quite a lot. It's neither as automatically left wing, and definitely not as community minded, as it was before.