Nate Boyer -- the former Army Green Beret who played briefly with the Seahawks -- says he doesn't exactly agree with Marshawn Lynch's national anthem protest ... but he fought for his right to do it!

Boyer's story is legendary ... he served 6 years with the U.S. military doing multiple tours in Iraq and Afghanistan before returning and walking on to the University of Texas football team.

After college, he signed with the Seattle Seahawks in 2015 -- and went through camp with Marshawn and Michael Bennett ... guys he really likes and respects.

So, we figured he was the perfect guy to talk to about Marshawn and Bennett both sitting for the anthem during the NFL pre-season games.

"They have every right to do what they're doing. I don't necessarily agree with it but it's their right and it's the right that I fought for."

He continued ... "They're not hurting anybody. They're not hitting women like some of these people in the league are doing."

Boyer -- who also consulted Colin Kaepernick about his controversial protest last season -- says what's more problematic to him is the state of the country.

"I think as a service member, it's more upsetting for me to come back from fighting for my country overseas to see how divided we are and how angry we are at each other as a country, I'm more hurt by that than somebody sitting down during the anthem."