J believes that people and Pokémon on an individual basis should have the right to choose whether to stay separate or not. He understands there are many on either side that would rather remain apart from the other party for an incalculable number of reasons, but firmly believes that the totalitarian approach of separating all people from all Pokémon is far too extreme and would lead to disproportionate hardship and suffering.

Plasma aside, Tina can't imagine a life without pokemon. In fact, half the reason she wanted to start her journey so eagerly was to explore the world, but knew she needed protection for the ease of mind of her family.
She does love pokemon dearly and despite all the difficulties that come with being a champion and maintaining her friendships, her teammates are always with her, they are her pillar of support.

If they truly wanted a life without humans, why would they always end up being bound together, after all?
(BW brainworms are understandable i have them too snfnsnfns)

Jin was raised around pokemon and unironically considers lots of them family. So the thought of pokemon and people being better off separated would be so strange to her.

Briar personally doesn't want people and Pokémon being separated because she sees them as useful. She doesn't think humanity would last without Pokémon helping, and humans also help Pokémon thrive in their environments, specially when it comes to human-made species. So yeah, they could possibly live without humans but wouldn't last as long because it's a symbiotic relationship.

... And also she's kind of fond of Pokémon so she can't imagine a life without her Pokémon.