This should be the top comment. You can tell from the article that the WSJ is trying really, really hard to push the 'intolerant liberals' angle. From what I can tell, the only person cited who really left due to politics was Thiel.
Well, this is indeed the biggest factor, no doubt. But it is just too obvious and far less interesting to debate than left/right flame war, which is an escapist fest.
To the extent tech workers are leaving Silicon Valley, I'm willing to bet the dominant factor is the cost of housing.