Light 'em up!
UPS should not be able to fire someone for inflammatory social media posts based on the simple fact that it's not a cardinal sin. But when things get to the point where the case is heard by a federal judge (or any judge for that matter) the risk of getting screwed over by our inept legal system is high.
He was fired for, or actually not reinstated, because he violated UPS's Anti-Harassment Policy by posting what he did.
It is happening everywhere. People are being fired, disciplined, or even not hired for what they are posting on social media.