Opposing points of view are important, that's how we improve ourselves and our nation. All those soldiers are fighting for that, and protesting is as American as anything. It's interesting though that people move the conversation to "these guys are disrespectful" ignoring the issues they are protesting (peacefully I might add), which many simply want to look the other way and pretend aren't happening. That's the real shame here.
On the other hand, if the NFL wants to punish players that do this I think they have a right to do it (within the law of course), just as fans have a right to not patronize the NFL if they object. The players who are protesting are using the NFL's brand to make their statement so I see both sides of that. It seems people forget that the right of free speech protects us from an oppressive government, not private citizens or businesses. It does not say "you have a right to free speech without consequences."
I recently saw where a little league football coach took a knee and had his team do it too. I draw the line here. I think kids should always be taught respect for flag and country. When they get old enough to understand the issues and how protesting the flag is not to be taken lightly, they can make their own decision on what to do. If it were my kid he would be off that team. Now if my kid said they truly believe they must protest this, and they are not doing it because the coach said to, I would support them as long as they understood and accepted the consequences.
A lot of these players do a lot for their community (and obviously a lot don't). In fact, what Kaepernick is doing is mostly for the black community (whether you agree it's the right thing or not it's certainly not helping his pockets). Besides, the history of Athletes making social statements is long. From protest statements by ancient Olympians and gladiators to Jesse Owens, Muhammad Ali, Jim Brown and many athletes from many other countries. Athletes have always used their notoriety to speak out on issues be it tennis shoes or social injustice, Kaepernick didn't invent this.