An overabundance of purity is hardly the country's problem.
Any more than an overabundance of purity is a problem in a barnyard full of pigs after six inches of rain.
It’s not really the “purity” that’s the problem. It’s what you do faced with the lack of it. If you go to battle, do you choose to go weaponless because the purity of a steel sword is less than what you hoped? You make do with the best you can get in the real world. Although a liberal Republican will be difficult to control, a Marxist Democrat will be impossible, especially since their voter base is not you.