Space colonisation with current tech isn’t a joke, but it is a folly in the sense of British Victorian-era aristocrats — extremely rich people doing fancy but not very cost-effective things.

Fusion isn’t necessary for this, however, as PV scales well enough for a Mars colony (don’t get me wrong, still extremal, but it could be made to work up to about Jupiter if cost of local manufacturing was not a limiting factor).

But: politics. Let’s assume every settlement on Earth has a corresponding space habitat (O’Neill cylinder or whatever) of the same population in Earth orbit. With this situation, rapid transport between any two locations is trivial enough that high school students could accidentally blow everything up up — I made an ion drive while at school (simple ones are easy) but orbital dynamics are counter-intuitive and not something a high schooler is likely to know, so a kid running one in space with that many large stations around has a high risk of causing a Kessler cascade.

Scale the hypothetical scenario up to a K2 swarm around the sun, same applies only with the risk of mass extinction on the home planet.

In either case it can be weaponised, and about 19 years ago a bunch of theocratic fundamentalists demonstrated that a small group of humans can be smart enough to cause enormous harm while also being dumb enough to not predict the consequences.