He never understood humans. When he first saw them, he was fascinated. They were so many, all different. Some with brown skin and some with white skin. Some were very tall and there were the ones who were shorter than him. They had different kind of clothes and ate different kind of food. They had technology he only ever saw at the dump, already broken. And their hair. That was the most fascinating. Long and short, blond and brown and black and red and... he couldn't even list all the colors. He only ever saw Master Splinters fur and that couldn't be more different. All in all, he loved humans. But then he get to know them.
Many humans say, that you only love someone as long as you don't know them. They were right. On their second night on the surface, they saw a robbery. A small group of humans beat up another one, took his wallet and left him to die. They didn't care that they were the same race. They didn't care that - hadn't the turtles taken him to a hospital - he would have died. They didn't care that his wife was dead and he raised his daughter - a small seven year old girl with blond hair and the cutest smile they have ever seen - alone. They only wanted money for beer. It disgusted them.
They were only four of their kind, so they got used to looking out for one another. But humans cared only about themselves. They wanted money, power, fame, beauty and stopped at nothing to get it. Not even the lives of another being, whether human or mutant turtle. They were disgusting.
And yet they continued to protect them. From aliens and from themselves. Because even if they were greedy and cruel, the turtles were not. They couldn't just let the humans hurt each other. Thus they protected them and hoped. Hoped, that one day they would see the error in they ways and live together in peace.