2 The Poké Ball is really Poké Hell
What's inside a pokeball? No-one knows. It's never been explained in an episode. The prevailing theory is that it's like a Tardis, with greater space on the outside than the inside. The truth however, is that it's closer to the ghost trap in Ghost Busters. The pokeball reduces Pokemon to "spirit energy" essentially killing them temporarily.
Once caught in a Pokeball they drift through an endless spiritual limbo until called upon to fight. But, hey at least they're not forced to fight to the death, right? Yeah, because death would be a merciful release from the undead hell that Pokemon suffer. And Pokemon isn't about mercy.
3 Meowth's tragic back story
Meowth's story is probably the most depressing in all the Pokemon universe. He was a normal Pokemon who, abandoned as a baby, ended up joining a street gang and falling in love with a cat called Mewsie. He couldn't provide her with the luxuries her human owner could so tried his best to be human to impress her by learning to walk upright on two legs and even how to talk
When he approached Mewsie she rejected him, seeing him as a 'freak'. But what did she know she was just a stupid cat. Surely the humans would be impressed by the only talking animal in the world, right?
Wrong again. Accepting that Meowth is a sentient being with a conciousness and rights would mean the fundemental destruction of a world based upon the subjecation, torture and murder of the only commodity in the Pokemon univere. So Meowth took the only job opportunity available to a fantastical talking animal in the Pokemon universe: a dangerous terrorist not accepted by polite society.