Unfortunately, I have no idea what motivated BrowserUk...

It is called cognitive dissonance, a recent study ("When in doubt, shout") explains his behavior well. He has been shaken in his belief that threads are the silver bullet for all things, because he knows now that his complaints from 2003 about "threads emulating forks in perl" (which he thinks was a conspiracy by the UNIX folks developing perl against Windows-users) are false. But he cannot let go of the belief that threads must be superior to forks. Now he rationalizes this by complaining that people run a "political" campaign against him. BrowserUk is a Born-Again-Threader. In his world, global warming is caused by forking and real computer science began when threads were invented.

It is understandable for someone who is getting old, but sad, I agree. I hope he does not drink industrial bleach because no one takes his FUD seriously.