I think there are also some topics where people are conditioned to respond emotionally. Once responding emotionally of course a fair reading is out the window.

I do think there is a lot of silence due to social expectations, also probably many of the likes/shares with little additional commentary come from such expectations. But IME the people that write the long rants tearing X person apart are either legitimately upset, or have an agenda way beyond trying to fit social expectations.

Of course you can't have mob justice without both the instigators and the larger crowd giving passive support. But I don't think it's accurate to assume it's purely people wanting to fit in. Many of the cases that gain traction have an emotional core.