get corrupted
Examples
A politician's goal is always to manipulate public debate. I think there are some politicians with higher goals. But all of them get corrupted by power.
I think it's very easy to get corrupted.
Many cults start off with high ideals that get corrupted by leaders or their board of advisors who become power-hungry and dominate and control members lives. No group with high ideals starts off as a cult; they become one when their errant ways are exposed.