How about speaking to HR and taking them through what the site is for, why it benefits them ENORMOUSLY, how they can be seen to contribute/add to the site but spending a moment to actually do their homework instead of blindly and ignorantly overreacting?
Seriously if all they think their job is is to watch a bunch of web filters then perhaps they should be recruiting for better people for their own jobs - businesses are about communication, insist they spend a moment or two of their time doing their job and they should see how foolish they're being.