Fairly straightforward stuff from Balls - all oppositions have to be seen to moan a bit about big infrastructure projects that will take years to build (like another runway at Heathrow) - knockabout politics.
If he can promise to deliver on HS2 whilst ensuring that the costs are well looked after then I don't think anyone can complain, can they? Well, almost anyone...
I've said before that I expect a majority will be against HS2 at the moment - like people are generally against long term infrastructure projects with little "jam today". Although of the two polls referred to in this thread, the "anti" vote has come down from something like two-thirds to 55% in a couple of years, which may suggest that it'll become more popular as it becomes closer. The question isn't how we deal with short term public opinion (which would probably mean Jeremy Clarkson as Prime Minister), its how we deal with long term problems. Apart from the "lets build a new railway from Sunderland to Blackpool" suggestion that one poster made, I've not seen a lot of alternatives...
Just a guess, but maybe they've stopped building high speed lines (apart from the ones that they are still constructing) because they've got a lot now, and there becomes diminishing marginal returns after a while?
You could argue that we in the UK are "no longer investing in Motorways" - doesn't mean that Motorways are a bad idea or that any other country should shun Motorways?