Well in this country it seems to cross the line when someone with no sense of humour and a loud voice notices it. Remember the Chris Morris Brass Eye scandal? Where a programme poking fun at the media hysteria over crimes involving children came under attack and attracted - guess what - media hysteria. But Channel 4 has some gumption - and a legal department, and if necessary deep pockets.
The satirist who put up http://www.thinkofthechildren.co.uk/ has the gumption, but probably not the legal backers, so when 'several' complaints thought it was 'inciting others to engage in mob violence' rather than parodying those who do the Metropolitan Police and the Internet Watch Foundation asked them to take it down. With little protection for free speech in the UK he decided to do so. Any freedom-loving non-UK Web masters feel like giving the censors one in the eye?