For my money, it seems to be proof that if the media drum up immense hysteria and potential hatred for their own various ends, some weak minded and potentially violent fuckwit with soak it up and do something terrible.

I agree to an extent. It's not just the media though. You are probably familiar with this quote from Britain First leader Jayda Fransen:
“They think they can get away with ruining our country, turning us into a Third World country, giving away our homes, jobs and heritage, but they will face the wrath of the Britain First movement, make no mistake about it!
We will not rest until every traitor is punished for their crimes against our country. And by punished, I mean good old fashioned British justice at the end of a rope!”
I'm sure you can see how this might inspire some people to take matters into their own hands. It looks like this guy may have toyed with far-right ideas for a long time. The hysteria of the last few weeks probably made him snap.
But that doesn't make it an unfortunate accident. We do have this level of extremism in our society now and to me, those who incite others to become violent are as guilty as the perpetrators themselves.