It's not a black and white issue (as in simple right/wrong). I understand the racial injustice protesting, but try that at your job and see where it gets you. So while I sympathize with their cause, they are choosing the wrong venue to do it. Much like I don't like to go to concerts to listen to someone go on and on about some cause they champion. I didn't pay money to be preached to.
Now, having said that. Trump is 100% wrong on this. This is free speech, he has no say in it. I do agree, that it should be up to their bosses to decide to 'fire' them should they choose to because they are doing it at work. Regardless, for him to twist this statement into an attack on American values and veterans pisses me off to no end. What would he know about fighting for his country? He's using the idiots of the countries blind nationalism to divide this country even further in every possible way. The president should not be dividing the country every other day. He should be uniting the country. Not only that, with all the suffering happening right now with all the hurricanes, this idiot has better ways to spend all his energy than arguing with the NFL.
As far as I'm concerned, if that idiot can be allowed to spout off on twitter constantly falsehoods, etc, he has no say in what anyone else does. He only cares about his own freedom to speak his mind, not anyone elses. He is a true hypocrite in nearly everything he says. He needs to be knocked down a peg or two.