Some Pokémon items, like Pokeballs, are obviously man-made. But some items obviously come from Pokémon—and it's probably not a stretch to think that collecting these items in bulk can have some ugly consequences.
The Pokémon series has touched on this idea, somewhat. Remember the Slowpoke Well, back in Pokémon Gold and Silver? If not, here's the quick version: at one point during the games, it's revealed that Team Rocket are cutting off the tails of Slowpokes. Why? Because they can sell Slowpoke tails at an absurd mark-up. The player, hero that they are, puts a stop to the evil venture—and thankfully, according to Pokémon lore, Slowpokes can indeed grow back their tails. Still, it's kind of morbid to think about, no? What jerks!
Pixiv user A舎長 has drafted up some rather haunting illustrations that dwell on the idea of humans harvesting Pokémon for items, with each image campaigning for the end of poor Pokémon practices. Surely we don't need to kill or harm the Pokémon to enjoy their items, right? Heck, do we really need the items in the first place? Obviously, this might be taking Pokémon too seriously, but it's still interesting to think about what kinds of activism a world like Pokémon would have.
Some images to mull over:
Lucky Eggs: add 50% more experience points after a battle; are sometimes held by Chanseys.
Slowpoke Tail...has an obvious origin. Did you know that there's a restaurant in Pokemon X & Y that serves Slowpoke Tail? Because yes, people eat Pokemon. D:
Heart Scale: used to trade with an NPC, so that he can reteach a Pokemon a forgotten move. Sometimes held by Luvdiscs.
King's Rock: allows Slowpoke to evolve into Slowking.
Light ball: when held by Pikachu, its attack and special attack is doubled.