Voting the man rather than the party is high principle indeed. Unfortunately it seldom pays off. The "Man" you voted for turns out to have no principles, just a talent for persuasion that tops his opponent. Should a man with principles actually get elected, no sooner does he take his seat than the political equivalent of Guido and Nunzio come by and carefully explain his first choice to him: He can keep his principles or he can keep his seat, but not both.
Democrats have an unpublished agenda of "Power for me, but not for thee". Dissenters are summarily tossed under the bus. Republicans are a party on minimalist government and carry this philosophy through to party management. Dissenters are tolerated and become known as "Mavericks" (McCain) or "Moderates"(Romney) who go on to destroy any narrow margins of majority their putative party may hold.
Vote the silver-tongued devil of your choice, but in the end, you get the Democrat platform. Quickly or slowly, your choice.