About guns...how long ago were they invented, weaponry as a whole I mean, in our world? Quite a while ago, I'd say.
When man learned how to hunt, he invented weapons. So, yes, we had the technology for weapons long before we were civilized by modern terms.
When people realise something has little use, they get phased out really quickly.
Considering the fact that knives most likely still exist in that world, not really.
I think the problem a lot of people are having with the question of whether or not guns exist in the Pokemon world is that a lot of people don't realize that weapons are actually
multi-purpose. They're not just for warfare or human-to-human combat. As Buoysel pointed out, they're also for hunting (both in sport and necessity), and they can be for decoration (e.g., Swiss Guards carry swords and poles that are essentially for decoration, not practical combat use.) and self-defense.
Yes, it's true that Pokemon can and -- depending on how far back you think the use of Apricorn Poke Balls go -- have been captured for battle by the ancestors of the Pokemon world. Likewise, Lt. Surge reveals that they've been used in war. However, it's never actually explicitly stated that Pokemon are the
only weapons out there. (In the Surge example, he only mentions that his Raichu zapped his enemies into submission. We don't know if he killed them with a gun afterwards. Given the fact that he's an American soldier, I personally think he did.)
That's the other problem a lot of people have. They forget that the canon we see is usually through the eyes of a child (except in Colosseum, where it's through the eyes of a former Pokemon thief anyway). Because of that perspective, the world seems a bit more innocent, and a lot more seems to be centered around Pokemon. While it's obvious that Pokemon is a big part of that world, it's not the
only thing there. This probably also explains why we don't (or very rarely) hear about things like government (because I highly doubt that a sports league runs the Pokemon world -- given that this is like saying the MLB runs the US), school for those who opt to stay home instead of start on a journey, occupations that don't have anything to do with Pokemon, and pretty much everything else. It's possible that we don't hear about guns simply because they don't matter to the character we're playing, so they're left out of the storyline.
As for why evil organizations don't seem to carry guns, there's two possibilities here. The first is that you're a flipping ten-year-old armed only with Pokemon. Most likely, they're underestimating you. After all, a lot of them seem smug about your presence until you beat them soundly with your fire-breathing dragon. With no protection except a gun and at most six (not including the character) opponents to face, I wouldn't be surprised if they stood down.
The second possibility is the fact that the evil organizations are fairly weak to begin with. I mean, think about it. An entire organization beaten soundly by a single ten-year-old. How this happens logically, I really don't know. (I'm
still trying to wrap my brain around how Team Rocket managed to do that with flipping
Goldenrod City two generations ago. Largest city in Johto, and
no one except a
ten-year-old can free the city?)
But Negrek's already covered this rant.
I'm just saying that it's perfectly possible to create a fan evil organization that actually uses guns. After all, it's the sort of black market underground thing that a truly evil organization would want to invest in. And besides, it's not like guns would be used on Pokemon. Shoot the trainer first before he can send anything out. Boom. Done.
Also, people wouldn't really have usefulness with guns, even if they were attacked by wild Pokemon. Say, a non-trainer is attacked by a frisky baby Nidoran. Poisonous, yes, so you shouldn't touch, but if you shoot it, it'll probably die because it's pretty weak. Pokemon are supposed to live in groups, so a very angry mother Nidorina/Nidoqueen will most likely attack you in rage after you killed its baby.
This is getting into a different sort of logic that a friend of mine brought up concerning the games: why you never see Pokemon above a certain level in a certain area. For example, west of Viridian, you have a patch of grass with weak Nidoran in it. You don't actually see any Nidorina, and you certainly don't see Nidoqueen (which don't seem to exist in the wild). So, by game logic, you could possibly shoot a Nidoran and not risk the anger of a stronger Pokemon, but that depends on how you actually explain this.
Besides, by this logic, a trainer would probably be chased too for battling and capturing that baby Nidoran against the will of the mother.