If Croom had come in and done his best, thanked us for the opportunity, and been an ambassador for us, he would be extremely well liked by our fan base.
Instead, he was never appreciative of the opportunity and then talked badly about us after over paying him by millions for five years to underperform. Look at how Rick Ray handled his firing and Boomer handling his firing at UF. I understand it's personally difficult to fail the way he did, but most people don't get a seven figure consolation prize for massively failing. It's definitely a mark against his character that he wasn't able to act graciously.
He also put his loyalty to his friends and his mission to promote minority coaches above his responsibilities to his employer, and much, much, much more importantly, to his players. Players only get four years to play. You owe a good faith effort to them. Never attempting to get an OC that can run your system (or at least giving McCorvey a chance to run his system) and promoting Cheese to DC was not a good faith effort.
Neither of these are massive moral failings. The first would probably be shared by most people. The second was much worse, but still came from not horrible intentions. But they're certainly enough that he isn't owed anything by MSU fans.