[Casey6]

It does not mean he is evil just because he wanted to test it. It just means that he wanted to see if his invention really worked. And Aizen was the only person he could go to for test subjects. it is not unlike urahara to work with the insane...take Mayuri for instance, he was in jail because he could be a threat to the ss, but urahara had him released so that he could work with him. Was he evil for doing that? He could've thought the same of Aizen