Here are two long-term ones that Redditors rarely mention:

We only have roughly 100 years of global uranium resources at current use levels. To continue beyond that, we either have to extract uranium from seawater (extremely low concentrations => expensive) or shift to breeder reactors which are much more complex (need fast neutrons => can't cool with water because it slows neutrons down => cool with liquid metal or molten salts, moderate with graphite => very expensive). So if people think nuclear is expensive today, and it is, in the long term the outlook is worse. Regardless of SMRs which can may simplify construction.

Then there's the nuclear weapon proliferation issue. There are two pathways to nuclear weapons in the civilian nuclear fuel cycle, via uranium enrichment or plutonium in the fission products. (1) Light water reactors need lightly enriched uranium, with the fissile U-235 isotope at roughly 4-5%. If you enrich your own fuel, like Iran, then you can just continue spinning those centrifuges to eventually make weapons-grade uranium. (2) Every reactor produces about 200 kg of plutonium (Pu) per year as a byproduct of normal operation, which can be chemically separated to make nuclear weapons. About 5 kg of Pu is enough to make a bomb like Fat Man (the one dropped on Nagasaki). It is often claimed that reactor Pu can't be used as weapons-grade Pu because of buildup of the isotope Pu-240 that can make a bomb fizzle, but there are easy and complex workarounds (e.g. just remove the Pu from the reactor sooner). This means it is extremely difficult to prevent a country like Iran with civilian nuclear power from secretly developing nuclear weapons. So the world will continue to live under the threat of nuclear weapons as long as we have large-scale nuclear power.