The problems with these filters is that they catch things that aren't porn too. For example advice on safe sex.
Next thing you know, the government is going to tell me who to vote in and out the office.
That's a lot more sites than you might think.
But I'm not surprised it's already on the cards - this has been coming since the early 00s (e.g. the "usenet is CHILD PORN!!!!1!!" newspaper outrages, the Sexual Offences Act 2003, etc.)