Ideally the game is about whatever you want it to be, although I can't remember a time where I played it as "colonizing and conquering." Usually there was some justification for killing things, beyond wanting their stuff, if only under the guise of "evil." But I've never played D&D in such a way that you go find a dragon who is nice or not bothering anyone, then kill it and take its hoard. Usually the dragon first took the hoard from a dwarven city it destroyed, or is currently terrorizing a region. Same with orcs; I've never played "let's go attack and kill that harmless orc village and rape the orc women and eat their babies." It has always been, "Orcs are marauding and attacking a defenseless village who call upon you to save them."
Now of course this approach misses nuance and isn't always grounded in realism. But it doesn't have to be. Fairy tales aren't, neither are myths and legends, or many epic tales, past and present. It is fantasy, and a game of myths and legends, archetype and imagination.
If you want to leaven your game with social and economic realism, more power to you. Maybe those orcs are marauding because their tribe is starving, and when the PCs find out, they're faced with a dilemma, a more complex problem to solve (can they find a way to facilitate the villagers and orcs peacefully co-existing?). Maybe when they get to the dragon's den, the dragon (believably) tells them that the hoard was reclaimed from the dwarves who stole it from her, while killing her baby dragons in the process.
Or maybe you don't want to play games that are based on combat at all. Maybe you want to play a pacifist cleric, who only heals or subdues, trying to re-channel and transform aggression and evil into peace and love. Nothing wrong with that.
All of the above implies: D&D is about a lot of things. In fact, it is about whatever you want it to be. That's the beauty of it. I'd suggest that we all stop insisting that it is only about a narrow band of things, things that we want it to be about. In truth, that is a rather colonial attitude: "Hey grog, no more senseless killing and meaningless adventure -- we're killing you and taking your stuff, because we find it offensive." The converse is also true, "Hey young 'un, your way of playing is silly and soft. There was a time when men were men, and women were women, and everything was clearly defined, with none of this funny business, which I don't want tainting my precious RPG books."
Personally speaking, I'm somewhere between. I am attracted to the mythic atmosphere of sword and sorcery, of fantasy lands dripping in forgotten history and arcane lore, with eldritch horrors, mysteries to be solved, adventure and, yes, combat as a major facet of the imaginative arena. But I also like a seasoning of complexity and nuance, that the monsters usually aren't just simplistic murder targets, but actually have their own ecology and raison d'etre. But yeah, sometimes they're demons from the Abyss, or a horde of undead, who just want to destroy everything in their path. But sometimes they're orcs with mouths to feed. I mean, maybe the orcs were pushed out of their homeland by elves, and are now trying to repeat the same to a local group of humans.
There are some aspects of D&D that are currently in vogue that I personally don't resonate with. I tend to cringe at the mention of the word "whimsy," generally don't like anthropomorphic races (except in rare occasions), and find that over-the-top thespianism generally isn't my cuppa. But I'm happy with the fact that WotC has broadened its umbrella to not merely accommodate, but support and encourage, a diversity of play styles, tropes, and character identities, especially when it means that more actual human beings can play the game.
I mean, via la difference! No?
