It’s a sane default to label power as evil in a society driven by greed, usury, and capital gain. Power tends to corrupt, particularly when the incentives driving its pursuit or sustenance undermine scruples or conscientiousness. It is difficult to see how power is not corrupting when it becomes an end in itself, rather than a means directed toward a worthy or noble purpose.

Labeling power evil is not automatic, its just making an observation of the common case. Money-backed power almost never works for the forces of good, and the people who claim they're gonna be good almost always end up being evil when they're rich and powerful enough. See also: Google.