Drawing a parallel between gun control and speed limits is a pretty broad step to take when looking at internet filtering and only one you would try and make if you wanted to install fear into your audience and you had no other particularly valid arguments for filtering that would stand up in their own right.
DIA already filters access to harmful content (kiddie porn and I think beastiality?) all of which only a very very small (and sick) proportion of society would argue against that sort of filtering, but beyond that and there are too many special interest / lobby groups arguing for or against any other blocks -
News sites, do we really want any Government to be able to say which news site we can and can't access?
Porn, ditto to the above, imagine if the Christian lobbyists controlled what could legally be viewed. Is porn necessary for a society, probably not, but is it bad or harmful? Thats another can of worms waiting to be opened....
Other than to promote special interests groups agenda's, I really can't see much of an argument for filtering...