I'm against fission energy, not against fusion energy.
In my mind, there are two unsolved problems with fission energy:
The first one is the safeness of the powerplants. It can be damaged by earthquakes / tsunamies, plane impacts, asteroid impacts, human faliure and technical failures, terror attacks and so on... In the case of a meltdown or something like this, landscapes becomes contanimated nearly for ever. Statistic calculations said, that every 20 years there would be such a disaster.
On the other hand, there is this radioactive special waste, without any possibility to storage it safely for millions or even billions of years.
So for fusion, I don't see this problems because there, the
radioactive half-live is not millions, but only hundreds of years and then it's possible to storage it safely.
The only big problem we have today is that we have no way to storage energy efficiently but if there would be a way, we can use wind and solar energy as well...
So for propulsion in space, im not against to use such methods if it is far away enogh from earth

I'm even not against to use nuclear power sources as it's done by the Voyager probes, Cassini and Curiosity and so on.
But I belive there are much better ways for propulsion thrusters as
Magnetoplasmadynamic thruster or such things.