It's an age old wisdom, isn't it? Power corrupts, absolute power corrupts absolute.
It requires very good education and constant reality checks to not be corrupted. And even then it's hard; a german MEP (Semsrott I think) once said that he will absolutely not do more than 2 terms as he already experiences the drag towards thinking of himself as somehow "better" or "higher" than others, which he is not. Yet there is no term limit.