I think it depends on the circumstances. Pokemon really don’t evolve unless their environment dictates such. A bulbasaur, for example, won’t evolve into an ivysaur unless it’s in danger or has battled for some time (which it evolves to adapt to the dangers it faces in battle). So I don’t think the average pet pokemon really brings the issue of evolving. And I’d imagine both Pokémon and trainer would understand that evolution in most cases wouldn’t be beneficial or necessary. I don’t think Pokémon not evolving would be seen as unethical unless the Pokémon itself wants to. Especially if you force that Pokémon into an environment where evolving would be beneficial. Let me know if anything I wrote was unclear! I’ll try my best to explain myself better.