Just to return to the question posed by the original post ...
I was initially strongly anti-HS2 for the following reasons:
1. It struck me as a Vanity Project, especially when I heard politicians saying things like "we are the only country in Western Europe without domestic HSR, blah, blah, etc etc". So what? I also saw the fingerprints of Andrew Adonis all over it; a man who - bearing in mind he doesn't ever seem to have been elected to anything of importance - seems to have had an awful lot of influence over public policy.
2. Over-engineered, both in terms of top speed and train length. [Though clever people tell me that a lower speed would harm the business case]
3. Too few stations - I felt strongly there should be a station to serve the Oxford area.
4. Poorly integrated with the classic network.
5. The major beneficiaries would be cities already doing well (London, Birmingham, Manchester, Leeds) and if they are advantaged then nearby cities (more in need of regeneration) would miss out (Wolverhampton, Liverpool, Bradford).
6. The proposal for Birmingham. Not sure what the answer should be, but a 4th city centre station seems plain daft!
7. Too expensive.
8. Environmental impact.
So why am I now (broadly, reluctantly) supportive? Because it's the only show in town. If it's scrapped it won't mean a showering of money on other rail schemes. It will I fear set back railway investment.
And - it must be said - some of the nonsense spouted by the antis has made me disinclined to be supportive of their point of view.