We still have a ways to go before we can start thinking about colonising another planet on a large scale. Nevertheless, unless there is some terrible catastrophe here on Earth that will knock us back a couple of notches on the Civilisation scale, I feel it likely that it will happen eventually.
The good thing about colonising Mars is that, unlike some of our own continents, there isn't the moral issue of invading someone's homeland (as far as the consensus goes anyway, assuming there is no life or no significant life on Mars). As a (presumably) uninhabited planet, Mars doesn't really belong to anybody, so possession isn't an issue. Some people would doubtless have their concerns about tainting a celestial body that has been (mostly) untouched by human influence for billions of years; they might consider our spread be the start of the human pests' invasion of the galaxy, or whatever. Or maybe they just don't want to see us potentially ruin the natural beauty of another celestial body.
If you look it from a scientific angle, it currently seems to be little more than relatively insignificant lump of rock with a pretty tall mountain and a nice red colour. Beneath the surface, it could be a valuable resource, so why not go there and make use of it? It wouldn't hurt anyone. No ecosystem to preserve, not much of an environment to look after. Heck, in a few hundred years we might have the terraforming technology to make it significant. As for the question of dropping nukes on Mars? Well, maybe double and triple check that we're not messing with any microbial life first.