It's not exactly an equal friendship for the Pokemon though, more a Master and Servant relationship. And practically everyone participates in blood sport aka Pokemon battle's or animal fighting.
Let's make no bones about it, being a trainer Pokémon is infinitely preferable to being a wild Pokémon. The ability to access Pokémon centers alone spike survivability, and makes it much easier for Pokémon to evolve since they can push themselves to their limits without consequence. Wild Pokémon die all the time, we saw that with big threats like a raticate and furret trying to take a bite out of Trixie. Her only other option was to ask for help from a Pokémon like Audino, who don't exist in Kanto.
If these were Mystery Dungeon Pokémon, sure, screw humans, but PMD this ain't.
Wild Pokémon are much more likely to live in mediocrity and fear, because evolving isn't a needed part of their development-remember old man Treeko from the anime? They can live out their natural lifespans in their base forms, so being in the wild just sucks. To level grind, you need to participate in actual life and death battles. If you can do that safely, well...Who exactly is gonna fuck with a well trained Charizard?
Trixie is lucky. She's bred from trained stock, and lives in Viridian Forest. Imagine if she was born somewhere like Mt. Silver.
It's like being a stray dog. Sure, they're free, but that just means that they need to steal and kill to survive. If they get torn open, it's game over. Trixie would be dead herself if it wasn't for Ash saving her.
Pokémon can also leave their trainers whenever they want, unless you subscribe to the theory that poke balls make them friendlier.
Even then, most people who live with Pokémon aren't Pokémon trainers, or at least, the kind that participate in official League matches for. Uh. Money probably?
The vast majority of people in the anime aren't like this. Coordinators are equally as populous, but people who use Pokémon for work or companionship far outstrip them. Gardeners, librarians, nurses, archeologist, magicians, Pokémon are involved in a vast array of occupations and multifaceted relationships with the people around them. Heck, trainers don't exist in the Ranger Regions of Fiore, Almia, and Oblivia. Or as an even better example, Rime City. I'm sure there's someone out there who could appeal to Trixie's goblin mindset.
This is all fairly pointless however. Pokémon has enough different continuities and ways you can tweak the setting that anything is on the table. We don't even know if this is anime Ash or Electric Tale of Pikachu Ash.