It was more than a mean word. A man aligned with with those who regard themselves as inherently patriotic & respecting of the armed forces calls a disabled veteran a "coward".
Not just a mean word, but the worst word you can use against someone in uniform. His thoughtlessness exacerbated by the fact that he himself did not serve.
& it's not just the word, but what it implies, namely that patriotism for people like Carlson assume is nothing more than a self-serving facade. That what really matters to Carlson is fulfilling his own ego needs.
I don't know you, Mr. Lorton, but I'm positive you would not call someone like Duckworth a coward, however much you disagreed with her or found some position of hers reprehensible. Because there are degrees of hypocrisy we avoid at all costs.