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N.Y. Giants star Jonathan Casillas thinks Jim Brown and Ray Lewis' meeting with Donald Trump was a great idea 'cause it opened up lines of communication with the soon-to-be prez.

Casillas -- a 2 time Super Bowl champ -- is aware of the Trump haters ... but says, like it or not, he's gonna be POTUS, so America must get behind him.

"We have to accept him and we gotta be able to support some things that maybe we don't agree with."

As for all the people criticizing Lewis and Brown for taking the meeting ... J.C. strongly disagrees.