Give me a scenario then. Because I'm only seeing three instances where your pet could get hate from a mob it wasn't already fighting:
1) Your pet was fighting a mob, and another mob linked with first mob. Said new mob attacks your pet, and because of how the enmity system works, your pet could switch targets if this new mob does more overall damage, etc. This is player error because you didn't move your pet away from potential links.
2) Your pet was fighting a mob, you got aggro, and you used your pet to get aggro off of you before switching back to the original mob. Again, the enmity situation, and your pet could change targets. This is still player error for not avoiding aggro.
3) The rare cases where mobs aggro pets. I don't remember specifically but I've seen one or two instances where there are mobs that will actually aggro your pet. I think one of them was an Assault mission, I can't remember very well.
Look, I won't deny that maybe I'm misunderstanding the situation you're coming from here. It's possible that you and I are on completely separate trains of thought. But until you explain it more coherently and in a clear fashion, say, give me a scenario so that I may see where the misunderstanding may be, I'm going to say that the whole hate situation is reasonable provided you pay attention to reduce your own error as much as possible. Not saying people are perfect - I know I've done every one of these situations and died for the first two at least a few times - but you can still actively work to improve.