HS2 is perceived as a vanity project and maybe at the scale it's being pitched, ie £50m's worth, perhaps it is. But the project is driven by a need, which is simply that the existing railway has no more room for growth - already the ORR is refusing access for extra services. And upgrading the existing railway just won't do. The West Coast upgrade started in 2000, has cost £10bn, still isn't finished and the extra capacity it bought has already been used up. It was also incredibly disruptive, meaning bus journeys for passengers every weekend and for extended "blockade" periods.
So what's the answer? A radical rebuild of the M40 maybe? Although that would probably be in the same order of cost as HS2 and just as ecologically damaging, there's more chance of that happening because it benefits everyone it passes, and living near a convenient access point increases one's house price no end.