If he were in an ideal world, making common cause with others in order to achieve the good would not require our sterling leader to become complicit in corruption. But the real world in which he must operate is far from ideal. And among the others with whom he must make common cause there will be some who are corrupt.
A prototypical instance of this is the need, in World War II, for the democracies to make alliance with Stalin, a tyrant on whose hands was already the blood of many millions of his own (Soviet) people before the war had even begun. Another instance is how the creators of the New Deal required as allies the segregationist powers of the Jim Crow South.
Such instances could be multiplied almost endlessly.
This, incidentally, presents one of the greatest challenges facing citizens in their search for good leaders: how to differentiate between those who indulge in corruption because that suits their purposes, and those who participate in corruption as the necessary means of accomplishing truly good purposes.
So we have a fourth dimension of the relationship between power and corruption. Lord Acton is probably right that power tends to corrupt, and Brin right that power attracts the corruptible (and the corrupt). And power also affords people the opportunity to show the corrupt tendencies they'd previously kept hidden.
And finally, participation in power also requires even the uncorrupt to participate in the corruption of the world.
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