The corollary to this that remains unspoken about the OP's thesis is: because of the mass reach of the major platforms, the "toxic" effects now have escaped being an internet-only phenomenon and now are manifesting in meatspace.

It's overly reductionist to attribute Trump and Brexit just to online trolls, but it's folly to ignore their effect at the margins (because both Trump and Brexit were relatively close calls, influencing a 5% middle ground definitely mattered).