That depends on whether or not the inventors are aware of the fact that their tech likely will never work.
In that case it is fraud. In the other case it is simply some group of people that are very much ready to believe their own story and successfully transmitting that enthusiasm to investors. I've seen a couple of cases like that and it always makes me sad that reality will shatter the dream ('wouldn't it be nice if?', yes, but that does not automatically mean that it is possible...).
More often than not charisma plays an important role in these exercises in wishful thinking.
If the purveyor of new, unproven tech is aware that it does not work there is yet another class of character, the ones that think they're only 'faking it until it will inevitably work'. Just one more little kink to work out and then all the reasons to fake it will disappear.
The only ones I have no compassion with are the cold hearted fraudsters who dream up their schemes knowing full well they'll never deliver. Those are - fortunately - quite rare.
A fool and his money.