Thanks Amy!
I know that Hagrid was very happy growing up with his Dad, and his Dad loved him dearly. I guess it bothered him that his Mom left, and like all of us he wanted to know the reason why she left. While his Dad did everyhting he could for him, he still missed his Mom.
I guess being around his Mom, who was a giantess, showed him that appearances doesn't really determine how dangerous something is. His mom was a giant and his dad loved her dearly. He was fond of his mom, so, Hagrid learnt not to judge any creature by size..
I also think that because Hagrid didn't have many friends at school, he spent his time caring for the creatures that were neglected and disliked because of their size, just like him.