I don't think anyone should "shut up and tow (or toe) the party line", but I do think their dissent should be constructive to the cause they claim to support (conservatism in this case).
I fail to see how bashing the only person in a place to advance the cause you claim to espouse, and casting a dissenting throw-away vote can be construed as standing for conservative principles.
Because in my opinion he is not advancing the cause so I might as well consider voting for someone who would.