The biggest, and most damaging effect HS2 has isn't one that is inherently obvious. It's a rather more insidious, long-term effect – that of continuing 'London-centricity'. The entirety of HS2 is designed simply to connect major cities to London, and make commuting there and back quicker. Why is this a problem? I hear you cry! Well, by constantly encouraging people to commute to London you create a number of problems...
1) You continue to make it exceedingly expensive to live in. Living costs in London and the suburbs around it are already significantly higher than those of the rest of the UK, and by channeling more people down from the North on HS2 these costs are only to rise even further
2) We end up with London as our centre of industry (which it already is now, but to an even greater extent) but with a few 'favoured cities' elsewhere. Why locate yourself in a city that isn't on the route of HS2? Why bother to build your offices in Liverpool, or a factory near Leicester when you're actively going out of your way to avoid the 'benefits' of HS2 if you do so?
3) You make it harder for people to commute from cities that are currently on the ECML or the WCML, as the services running through cities like Coventry will be reduced. Why? Well, if you're actively pushing everyone on to HS2 then those trains will be emptier, thus pushing up ticket prices on other routes, and reducing the number of trains running. It might make it easier for a businessman in Birmingham to commute to London, but far harder for anyone in the rest of the Midlands who now have to go out of their way to change in Birmingham to take HS2.