But you prove my point. A Republican voter who refuses to vote Republican in a particular election (out of spite or whatever) is making it that much easier for the Democrat to win. This is simple common sense.
That voter has left the party. If someone leaves the party the best you can hope for is that he stays home or votes 3rd party. Would you rather him vote for the Democrats?
The goal is to stop the person from leaving the party in the first place.