Throw enough subsidies at anything and you can claim it works. When I was in Europe I had heard that the best way to get around was still plane, the HSR was only economical if you bought a monthly pass.
Apples and oranges -- unless you can also buy a monthly pass for plane travel. But for those who use the train frequently... why not?
You have all that infrastructure built and it still doesn't even get to half of the cruising speed of a plane.
True. But then, you can't get an airplane to drop you off right in the middle of downtown Paris, either. Just like any other big city, it takes a good 90 minutes to get from downtown Paris to Charles DeGaulle Airport. Last summer I took a high speed train from London to Paris. Comfortable, clean, convenient.... and 2.5 hours. By plane, it would have taken me that long just to get to and from the airports.
Even in the US Amtrak is almost never as good of a deal as a plane and also quite slower.
The cost/benefit analysis for passenger rail in the US is significantly different than for Europe, however; and even in the US the case for rail along the Eastern Seaboard is far different than for transcontinental travel.