You make a good point, but billions have been spent researching fusion power. One of the problems is that advocates often work against their own interests by shouting down any attempt at conversation that does not fit their narrow parameters. Any one who questions a deeply held belief not backed up by facts and reason is met with derision and ridicule.
There are a lot of highly competent US scientists and engineers who want fusion to work and have a lot of money to show that it can work. So far they have failed to show it CAN work.
If someone wants to build the star ship enterprise it is not too much to ask that they show that they can actually make dilithium crystals and that when put in a warp drive you actually produce some propulsive thrust and to hold off the intergalactic mission planning until they show at least that much.