I certainly didn’t mean to say the fusion bubble would be just hot air. Bubbles are typically associated with technological advancement. The stock market goes a little crazy and lots of money floats around looking for every opportunity to invest in the new big thing. So these bubbles have a useful purpose, in that they bring very rapid development and adoption of the new technology.
But all that investment is high-risk. After a while the mania passes, a lot of weaker firms fail, and a lot of people lose their shirts. But you’ve still got the new technology, which has longer-term benefits to the economy. In the case of fusion, that benefit will be enormous.