Party politics is not the struggle of good vs evil
But a confrontation of one set of reasonable people against another set of reasonable people - both loyal to a different set of principles, that may be orthogonal to each other
The whole point of Party government is that reasonable people can disagree, and both can be right from the prism of their principle-set to which they're loyal
And this tribal loyalty is a counter-weight against individual discretion / brilliance which characterizes statesmanship
Parties curb statesmen, as statesmen can be morally unreliable
That's the Burkean thesis
Individual wisdom is unreliable.
Tribal loyalty is more robust