Accusing others of being witches shows off your own moral purity. It also gives a feeling of power, a critical mass of the American tech crowd comes from the PC left that is large enough to set off a mob. The ultimate feeling of importance comes when a witch is burned (fired from his job). PG is a poorly chosen target in some sense, since he will be extremely hard to fire - although public humiliation is also satisfying to SJWs[1].

It is not all bad. One of the classic phenomena of witch hunts is when the hunt comes back to bag an original instigator. This is rich in irony and entertainment value.

[1] http://en.m.wikipedia.org/wiki/Struggle_session