Of course, whether that's a good investment of resources right now is another question.

Even if we had no other goal than becoming an intergalactic species as soon as possible, we might still benefit from working on other things first.

You are operating under the rather naive assumption that the people and resources used in fusion research are fungible with the people and resources used in other things.

When you have a bunch of people who know how to build nuclear bombs sitting around with nothing to do, you damn well keep them busy before another country finds them a job.

For further discussion, we'd need to be careful whose perspective we are taking and what timescales we are talking about.

You seem to be taking the perspective of individual countries? And not eg humanity.

And timescales of perhaps decades?

On longer timescales: people don't get born knowing how to build nuclear bombs. They are trained up.