NBA superstar Isaiah Thomas says he will NOT be sitting during the national anthem this upcoming season ... but tells TMZ Sports he supports his fellow athletes for doing what they feel is right.

We spoke with the Celtics point guard about players like Marshawn Lynch and Michael Bennett staying seated over the weekend ... and while I.T. says he's not gonna join the movement, he understands the bigger picture.

"Stand for what you feel is right. I'm not going to do it, but that's those players' decisions."

Thomas also talked about the recent violence in Charlottesville ... and he wants to send a simple message:

"I just wish everybody would love and not hate."