I wasn't talking about legal or constitutional rights.
A member of a community accepts obligations to the whole beyond those defined and enforced by law. In a society composed of diverse individuals and groups, many with conflicting interests, an accommodation is necessary in which we don't aggressively push our own cause when that interferes with the right of others to pursue their very different agendas.
Instead, we designate forums in which conflicts of interest can be addressed - around a communal fire in a hunter gatherer camp, a gathering of elders in a village, the Agora in Classical Greece, a town hall meeting in middle America ... We create appropriate spaces for discussion and dissent; outside of those spaces the business of the society is allowed to proceed as normal. Without this restraint the life of the community is fatally impaired.
The actions of the NFL players violates that compact. The normal business of the community - watching a football match - is turned into an occasion of political dissent. Those who have contracted to watch a football game are forced into becoming unwilling spectators to a protest in which their values are insulted.
A belief that America is so broken that the social contract is abrogated might excuse the actions of the players. But these particular young men show no reluctance to profit greatly from that contract while proclaiming their disdain for its symbols.