I've came close. The Firing Line forum, years ago, back when they allowed more spirited discussion on their site than they do now.
Found out the hard way that the powers that be on that forum are firm believers in circling the blue wagons. Never actually insulted cops, or said anything anti-police. I stated how I intended to keep and make use of my rights if I get a traffic stop or license check. How I'd request a warrant, not allow a warrant-less search, etc.
Both times I got stern warnings, and was told that they do not tolerate "anti-police behavior" on TFL. I was told the 2nd time if it happened again, I'd be banned. They didn't have to ban me, I left.
TFL is a great firearms resource. if you need info, they're a great place to look. But the site is firmly rooted in the "cops can do no wrong" camp.