An animal has different emotional needs aside from the nursing aspect too

I'm going to point back to orphaned human animals.

here in Europe

Ok. In Japan they'll erase you from public records if you're famous and caught with cocaine, but fine you $10k if you're caught with under-age porn. Different countries, different cultures, different laws.

Your kitten might have had emotional trauma and behavioural issues, although this was the breeder's fault not yours.

Breeder? What breeder? It was found on the side of the road. Not all rescues come from breeders. They can be litters from ferals or strays, or just plain abandoned.

I would've agreed with you here if we humans couldn't cover another human baby's emotional needs

I feel that enough footage exists of monkeys adopting chickens to highlight this isn't a uniquely human ability. You honestly think cross species emotional catering isn't possible?

I think you're pretty black and white with the whole "it's not cruel to separate a mother from it's young" ordeal.

Ok. It's not inherently cruel. You asked a blanket, all encompassing question of "Is it cruel?" Not "Is it cruel in certain circumstances, but not in others."

I answered in kind.

You might as well of asked "Is killing murder?" at which point I would say "No, that's like saying immunisations which kill viruses are murdering the virus." because no, not all killing is murder.

That's what I mean by black and white.