Corrupted by power, Ha! It has always been humanity's objective to use power for selfish ends. The purpose of power is to advance the self.
I'd argue that liches actually don't experience any corruption to their minds. A lich still has their old morals, as shown by Barilzar and Aesliip. Of course, one thing you have to realize is that Random lich #55 may never have been of "good moral character." He may have been one of the meanest people on Tamriel before going Lich. Hell, morals change. That Lich may have simply changed his mind about what he thinks is right and wrong.