We are already building hydrogen cars. They haven't marketed it because they haven't reached the level of gasoline cars. But we will. Unless these "Don't try it's hopeless" types get their way.
I remember when it wasn't possible to get more than 200 meg on a PC hard drive.
Let's assume the average car gets 20 mpg at and gas is $1 per gallon if you remove taxes. That comes to a nickel a mile.
When your hydrogen scam can do that, it won't be a scam.
The key to hydrogen isn't fuel cells or hydrogen, but cheap nuclear power.