Sure, but you don't have to express yourself on twitter... you do that when you want to communicate something to all your followers.
> ...The gains are extremely low and this could cost him his job.
That's true of the tweet by itself. If sober reason was going to hold him back there would be no tweet at all.
Or you do it automatically and habitually. The brain to mouth filter and a brain to keyboard filter are similar, many people don't have either.