You need to look at the management's point of view. In the radio and TV business, ratings are everything. How much you can charge your sponsors for a 1 minute commercial is all based on ratings. How much did his speach damage his employer? That is the question. Also, was what he said truthful, or opinion?
So, we go to contracts. What did the DJ have as a contract? and how did the DJ represent the management when he made his statements?
I am surprised that the kick back from whatever he said on air generated that much protest, but I am very happy to hear it did. Philly is cesspool of anti's.
Free speech is a very good thing....unless it damages someone else. When that speech is made privately, it is not so much of a problem. If the speech is public, and that speech damages someone else, then it should not be allowed.
One quantifier here...that would be that the public speech that did damage someone else is true. Extreme example: If you say someone is a murderer, and it is not true, that is slander and not allowed. If you say the same thing about the same person, and it is true it is not slander.