If someone is expressing political or even religious views that are so extreme that they create a hostile work environment, I don't see an issue with firing them over it.
(I am not interested in debating whether or not Damore's views reached the "hostile work environment" threshold)
There is a process, and step one in that process is asking them to please stop sharing their views in the workplace.
Expressing extremely wrong views can't be the standard for creating a hostile work environment because people are wrong about a bunch of stuff and the only way to figure that out is to express the view and be told why it is wrong.
Particularly in the Damore case, the standard shouldn't be how a third party feels. There is a long history of seeing how that standard plays out, it'll end up hurting minority voices. The standard needs to be how a first party responds when asked to do something.