"[W]hat better way of providing automated defences at scale than by the major private providers effectively blocking their customers from coming into contact with known malware and bad addresses?"
What better way of allowing the UK government to censor what British people can see and hear on the Internet, without the huge majority of them having any idea that their Internet access is being censored?
And for those who have suggested this is no big deal, just wait. This is a case of "First they came for the communists", with a vengeance. Quite apart from the fact that this is exactly what the Chinese government has been doing with its "Great Firewall of China" - and getting it in the neck for alleged tyranny, totalitarianism and censorship.
Of course, how this policy would work out in practice does depend very much on who decides what constitutes "known malware and bad addresses [sic]". Previous draconian laws passed by the British Parliament were, we were solemnly promised, to be used only in the most serious of terrorist cases. A couple of years later, the powers were in fact being used by town councils to spy on what people put into their rubbish, how they kept their gardens, and other such personal and utterly non-vital matters.
If a law is passed establishing a "Great Firewall of Britain", we can be quite sure that within a couple of years literally thousands of government employees - from the Prime Minister to town hall clerks - will be contributing "bad addresses" to the cumulative DNS blacklist. Just like the current Homeland Security watch lists in the USA, thousands of items will be added every month, and nothing will ever be removed.
Indeed, people living in Britain may well find that, one day in the not-too-distant future, they are no longer able to read or contribute to Slashdot. After all, just think of all the contentious issues and worrying statements that are to be found on its pages! Some government functionary - or, perhaps more likely, an instance of that classic responsibility-diffusing mechanism, a committee - will take the view that it would perhaps be for the best if this rather dubious Web site were no longer to be accessible from the UK.