The Nazis almost built a working nuclear reactor.

[hunter]

4. Depleted uranium is used because there are huge stockpiles left over from uranium enrichment.

Natural uranium works as well in armor piercing projectiles. It's all about chemistry and density, nothing nuclear.

Uranium is toxic as a heavy metal, like lead or mercury.

By ethical measures there's not much difference between natural uranium projectiles or depleted uranium projectiles.

In a society that accepted nuclear power depleted uranium might be used as fuel for nuclear power plants. In that case it would be absurd to use depleted uranium in munitions since each gram of it has the potential energy of a few million grams of burning coal.