Most of a Pokemon's life is spent fighting, hurting others and getting hurt in return. That sounds like a terrible life to me. Is there some in-universe reason that Pokemon willingly allow themselves to be used and abused by their trainers in such a way?

Some argue that Pokemon are like domestic animals: They aren't intelligent enough to know better, just like dogs and roosters in fighting rings. However, this doesn't seem to be a strong argument for two reasons:

-Firstly, Pokemon are highly intelligent and have their own language. They are even capable of some degree of advanced logical reasoning, as can be seen when Pikachu discussed the possibility that it was dumped by Ash with other Pokemon in the 'Electric Tale of Pikachu' Issue 07.

- Secondly, unlike domestic animals Pokemon have incredible powers that dwarf those of humans. Seriously, how would a human intimidate a Legendary Pokemon capable of altering time or space into doing its bidding? Or a Charizard capable of "quickly melt(ing) glaciers weighing 10,000 tons"?

As such, are there in-Universe reasons for:

Why Pokemon obey the humans that forced them into slavery?
How Gym Badges force a Pokemon into obeying a human?