Can we nuke someone today and get away with it?
Not practically, I don't think.
The nukes we have are bigger, the radioactive particles would spread too far, inevitably there would either be an ally or someone we didn't want to antagonize downwind or downstream who'd be really p.o'ed at radioactive fallout or radiation rendering their water source(s) unusable.
I think we'd honstly have to get launched on first by, say North Korea (the Iranians are not insane enough) before we could get away with nuking politically.
Speaking ethically, not practically, I'm not sure there's any good reason to use them currently.
I say this thinking that full-out nuclear war would kill all of us, kill most of the vertebrate species on the earth if not all, and potentially even take things back to bacteria. It would be pushing the reset button on planetary evolution.
That's very immoral to even risk the remote possibility of. My own ideals include survival of my species, survival of other species, protection of the biosphere, and our eventual movement into space...so a nuclear war for the short-term goals of a country, when compared to a species imperative like get off the rock, figure out how to colonize the solar system...well, the long-term survival of the species ought to come first.
Hiroshima and Nagasaki I'm prepared to accept as a somewhat special case. This is why: We had two bombs, and only two. They were a lot smaller than the current thermonulear weapons. We had very little idea how dangerous radiation/ radioactive fine particulates were back then. We thought we'd kill more of us and them in a conventional invasion.
I'll give it a "very vaguely moral." At the moment. Unless someone comes up with a really good argument otherwise.