The world of Pokemon is a world of animal cruelty where humans force unique and fascinating animals to fight for fun and sport.

First, it's stated in the games that Pokemon die and can be killed (the Lavender Town arc), so it's entirely feasible to think that some Pokemon battles can result in death through accidental use of overt force.

But even if you don't believe the above is possible due to X reasons, Pokemon are canonically being "poisoned," "burned," and "hurt" in the games, to such a degree that they end up "fainting." There's no two ways around that.

>But it has been stated that Pokemon naturally enjoy fighting for some mysterious reason!

Even ignoring the fact that the Pokedex states that some Pokemon "basically do not fight" in their natural state (such as Leafeon), it is one thing to allow Pokemon to fight in nature and it is another to capture them and force them to do so whenever convenient. Just because you enjoy doing something doesn't mean it'd be okay for someone to force you to do it for their entertainment whenever they please, especially if this activity involves risk of injury.

>But Pokemon form strong bonds of friendship with their trainer, which shows that they enjoy their situation!

Animals can become very attached to their master as a result of conditioning and fear. A sense of attachment and closeness does not mean that the Pokemon is necessarily happy with its situation. Pokemon are also shown to be relatively smart creatures who resist capture (I wonder why) and many species may know that bonding with their new master is their best chance of staying out of harm's way.

Pokemon is fundamentally inhumane and cruel. It's okay if you want to keep playing, but you cannot prove me otherwise.