That's not true. Coal pollution and deaths are guaranteed mainly by economic disincentives to using clean coal technologies. Even mercury and CO2 emissions could be captured. But then, that would likely make solar the clear choice.
Because solar is intermittent, and isn't practical at all in many parts of the world. The true environmental impact of nuclear is also arguably less, since solar requires a lot of space per watt produced by comparison.
Next-gen nuclear reactor designs from Thorcon Power, Terrestrial and others are very near to perfectly safe, and also produce much less long-term nuclear waste than current designs. There will be an ongoing need for clean, high-density electricity sources.
> Because solar is intermittent, and isn't practical at all in many parts of the world.
The solution to that is simple, use less power at night. I.e. don't make so much aluminum when there is no sun or wind. We could decide as a society to trade a few percent of our wealth for using much less coal and nuclear if we wanted (and if our society were organized in a rational fashion).
Also: don't heat with electricty, but use e.g. solar thermal or geothermal power.
Night isn't the only source of solar intermittency, overcast also has a large effect. Solar also isn't cost effective at higher latitudes. When people are freezing to death, your simplistic approaches won't appeal much.
Efficiency is great and should be encouraged. We still need increasing amounts of reliable, plentiful and cheap energy going forward. You may be willing to accept a diminishing standard of living, most are not.
Because solar is largely unsuitable for base load power stations. Only solar thermal with molten salt storage or a gas pipe nearby to run the turbine during the night counts for base load. Otherwise we are talking 0.2-0.25 capacity factors.