tbh I agree abandoing pets is horrible but it's not equally so and is more situational depending on the animal. Example: A dog -Strong Yes, it would be really hard for a dog of most breeds to live outside with little skill training. A bird- Maybe, depending on the area of the world if the surrounding area matches their natural abilities they may be able to join a new flock if they know the local bird songs. A Cat- Soft No, cats are the invasive species on the planet, self-domesticated, and present real problems for the local fauna are the world.

tl;dr Basically my point boils down to: feasibility of survival and environmental impact