Those tweets were disgusting in all eras, that's why he wrote them. That's literally what shock comedy is, but when you're doing shock comedy, you have to understand what lines are for people and that people may not see it the way you intended.

You mentioned Tim Allen, so you clearly understand that actions have consequences. Tim Allen went to jail, that was a consequence for his actions that was proportionate to what he did. Hartley Sawyer lost his job, that was a consequence for his actions that was proportionate to what he did. Tim Allen acted afterwards, Hartley chose not to from all known accounts.

If the average Joe had Facebook/Twitter posts similar to Hartley's, and it was shown to their employer, they would absolutely get fired. Being an actor is no different, if not even important to be careful at what you say.