I feel it is one thing to buy a house in the full knowledge that a railway line is already nearby
A substantial part of HS2 uses the alignment of the Great Central Railway, closed under Beeching. Many of the people who are complaining had bought a house which adjoins, or in some cases is on, the trackbed of the GCR. The GCR had always been seen as one of the less defensible of the closures: it was the last line from the north to London to be built, and had been built with the intent of high-speed running with a large, continental structure gauge and gentle curves and gradients linking eventually to a channel tunnel. Proposals to re-open it have been made on a fairly regular basis, and although the alignment has been substantially lost further north, the southern section was relatively complete and had started to be protected. A lot of the people complaining that it's all come as a surprise to them in places like Brackley would have done well to have paid a bit of attention over the past twenty years.
It's also slightly difficult to see what alternatives people are proposing. Building a high-speed line costs little more than building a "classic" line, and in some cases is cheaper (TGV stock doesn't tilt, for example, and TGV lines don't need to be compatible with other stock). The West Coast Main Line is full to capacity, and trying to mix goods, local and semi-fast commuting services and expresses on an infrastructure last substantially upgraded (and that very, very badly indeed) in the 1920s is never going to work well (which is why Europe doesn't try).
An attempt was made in the 1990s, which spent insane amounts of money (the "PUG2" project cost approaching £10bn) in the hope of delivering 140mph running and increasing capacity, but it failed. You can point to that as a reason to not trust the railways, but we all suffer: capacity on the London--Birmingham--Manchester--Scotland route is desperately short, as anyone who's got a morning train from Birmingham to London will attest. Even with trains at, or arguably beyond, the length limits of the infrastructure running every twenty minutes on a time-table that is horrifyingly fragile, the trains are full to capacity for large parts of the day. HS2 isn't needed for speed: that's just a handy side-effect that it's almost silly not to take while it's on offer. The main problem is raw capacity, which for practical purposes is still at the levels it was in the 1960s.
The alternative to HS2 isn't no railway, it's building another "classic" route for roughly the same money along the same or an adjacent alignment. It would be just as intrusive, almost as expensive and deliver less capacity (faster trains => less track occupancy => more capacity), and for what?