1. First of all, he has been sacked in most senses of the word. He's not legally an employee (a point I've already acknowledged) because ITV have used a shady employment practice to hire him, and it looks like they've used another shady employment practice to fire him. That's typical worker-boss relations given the scaling back of employment legislation over the past few decades.
2. ITV have said he's been sacked for his comments. They didn't say whether it was his political views or his criticism of Clarke. The Huffington Post broke the story and they seem to have decided it was for both of those reasons so not just the 'fucktard' comment. Either way, I think it's disgraceful that he's been sacked but especially so if the decision is partly informed by the expression of his political views.
3. Yeah we can talk about all those other instances as well if you want whether that's blacklisting, McCarthyism and everything else because I have never been a supporter of an employer's ability to summarily dismiss people for their political views or if they praise or criticise a public figure - something which we all do. I've always been a supporter of an employee's rights to express themselves freely if that expression doesn't affect their ability to do their job and nothing this director has said has affected his ability so there will be no hypocrisy/backtracking from me if someone gets sacked for saying the opposite political opinion.
4. Quite frankly, I'm disgusted and always have been by the support for 'freedom of consequence' and any form of cheerleading for bosses being able to sack people on a whim but as has already been noted by
@squirtyflower , there does seem to be a resurgence in those views hence why all those academics signed that letter in the OP.