Never, never, never, never, never-ever - NEVER feed a barn cat. First one was okay... it's still with us - someone's former housecat and mostly alright, but clingy as Hell even though it catches its food. Spends most of its day outside our door, meowing as loud as able. Second was a bit too aggressive, but tolerable and fairly non-clingy... ended up pregnant - 5 disappeared, one was dead in a flowerpot, cat kept running away from the kittens and called our bluff of not wanting to take in 6 new cats. She visits every few weeks, but has mostly moved on. Third was a psycho missing half its tail and a toe (which it made up for by having six toes on another paw). Scratched daughter more than a few times and bit hard into flesh when happy. He was kicked out with prejudice. There's a fourth one - enormous, mangy, orange fuck - who occasionally glares at us at a distance, like it's casing the house and plotting to murder us in our sleep. He'll attack any other cats which come near it.
Dogs are too loud, needy, and the one we have sheds at an unbelievable rate (takes a while to get its fur out of the carb's air filter on the mower). Ferrets are kind of fun... wouldn't mind having a ferret around... maybe a trained guard ferret. Nobody'd expect a ferret to run up their pants and bite their balls off. -Or just a few fish.
My experiences are the complete opposite!
But an agressive cat, a cat thats agressive towards humans and harms your family, I think it should be put to rest, in general I think if animals are treated with care, respect, love and patience, their behaviour will also reflect that, on the other side, if they're treated badly, they will also become badly behaved.
I think the period when the animals are small is the most important period in their life, given enough love, care and attention, they will form into being great pets.