There are serious problems. If you subsidize an industry that is no longer functioning, it's sort of like in permanent receivership. I'm not talking about the Canadian situation. But if you have a theoretical situation where an industry is in permanent receivership, the only way it can survive is to have more money pumped into it. At some point you can't continue. It's not feasible. When you have a growing economy you might be able to tolerate it for a while, but eventually something has to happen.
This is not the situation in Canada. Very often the money provided to the industry is in loans that have to be repaid, so it's certainly not the situation here.
At various times the industry was in dire straights. That is true. In the mid-1970s the government took over de Havilland and Canadair in order to keep them from disappearing altogether. It turned out to be a good decision, but there was a period of five to 10 years when it was a fairly closely run thing. It might have gone sour, but in this case it worked.
Very often you don't know in advance whether something will work. You think it will work. You're pretty sure it will work. Then something happens like the Concorde, and the world changes. It has to be a policy decision, but I'm afraid I can't go into detail because I'm not an economist.