Yes, we can't do fusion in any practical manner at the moment, but we can't do fission scaled-down either: if you disagree, please show me an example which is economically successful. US Navy ships don't count (not "economically successful"). Someone actually tried building a fission-powered commercial cargo ship ages ago; it didn't last very long. It cost so much to operate that it was retired in a few years and sent to a museum in Charleston SC. With absurdly expensive fuel, nasty waste which needs to be disposed of somehow, and extremely dangerous operation requiring highly-trained personnel, fission plants only make commercial sense when they're scaled up to gigawatt scale power plants. Fusion plants may not be practical yet, but they'll never be practical if no effort is spent on R&D to make them that way.
Scaled down fission reactors like the Toshiba 4S can be sized to power an apartment building or city block. There are numerous micro reactor designs available and a variety of companies working to try to create a market for them.
When it comes to terrestrial reactors then fusion reactors will be enormous (need to generate a lot of power to compensate for the huge risk and the massive costs that it will take to build them) and if you are talking about putting reactors in space then it is foolish to consider anything but fission for at least our lifetime.
This applies to things like ships and submarines, and to spacecraft.
So yeah, solar/etc. sounds great in an ideal scenario in a perfect world, but what if you're not on this world? Solar power isn't sufficient to do serious mining operations in the asteroid belt or to redirect a large asteroid threatening to impact the Earth. It also won't power your aircraft carrier or cruise ship. A clean source of nuclear power would be ideal for all these things, if we can figure out how to make such a thing work.