I'd consider them equally as silly, considering we're actually capable of launching rockets into space yet the closest we've gotten with a space gun is a measly 180km apogee @ 3.6km/s[0]. The original question was why we don't send our nuclear waste into space. We can't send our nuclear waste into space using a rail gun because we can't currently send anything into space with a rail gun.

Otherwise here's a good discussion on the viability of space guns: https://space.stackexchange.com/questions/2370/what-technolo....

[0] https://en.wikipedia.org/wiki/Project_HARP

It's cheaper and safer to store it in deep crystalline bedrock. I guess if we geologists can't convince we the people of that maybe the railgun idea would work, especially if you could hit the sun where the fast fusion neutrons would consume the hell out of it.

What if it fails and the waste falls back to Earth spreading over inhabited areas or agriculture/fishing grounds? It's a bad idea to begin with.