Read every prominent terrorism/extremism/etc. researcher, every law enforcement person who gets into this, etc. They always say one thing, keep the site up and let the people keep posting. The reasons are numerous. Never do they say "if a threatening looking post is up for fifteen minutes wipe the entire site off the face of the internet" and certainly do they never say "and immediately go public about this in The Washington Post."
An actual terrorism website wouldn't get treated this way until the feds actually took it down, that makes it obvious it's clearly about the content of our speech.