I do not think there is any boxer in history that was universally liked. Your first question is difficult to answer because of the word "some". You should have used a better term; one that could be measured - i.e. why are there more SRL haters than admirers

Over rated? Was he not an Olympic Champion who made a good transition to the professional ranks? He fought against the best during and after his prime. He won a lot and lost some. He was a great boxer, no question. Hall of Fame candidate? Probably (unless he already is...please correct me if so).