Mission creep
Yeah, we need to block kiddie porn. And fake kiddie porn, and any promotion thereof... and that Wikipedia article with that dubious album cover, can't be too careful you know.
Of course we'll be blocking really weird hardcore adult porn, you don't have a problem with that, do you?
We need to block piracy sites now, wouldn't want people depriving musicians of their hard-earned. And hacking-related sites, obviously. We might as well block warez sites too, while we're at it.
We might as well block all the porn you can't buy on DVD too, why anyone would want to look at that filth is beyond us. Again, you don't have a problem with that, do you? Good.
Apparently on some forums and 'news' sites people are saying we're blocking too much stuff, we might as well block those forums too, for the sake of social harmony.
We've found there's some sites spouting dubious political ideas out there, fundamentalist Islam, socialism, libertarianism and so on. Hardly Lib/Lab/Con, is it? Blocked in the interests of stability, of course.
Hmm, we've logged that you've been trying to circumvent the blocks. You do realise they're for your own protection? We can only assume you've been trying to look at kiddie porn. A white van will be along shortly.