I can't think of any respectable reason to vote for John McCain in this election, but, according to the polls, 90% of Republicans will vote for him. Is party loyalty a good enough reason? It is a valid reason to support a candidate generally; I certainly weigh ideological proximity more than apparent objective competence when I decide whom to vote for. But this kind of brand loyalty must have some limits. So the appropriate question is, if a Democrat comparable to McCain ran against a Republican comparable to Obama, whom would I support?
To concretize this question, it would be useful to come up with an analogy involving real politicians. That is difficult and subjective, but I think I have come up with ideological mirror images that aren't too distorting.
McCain is a war hero (at least in the sense the term is commonly used in contemporary America) who has, as a politician, been reliably conservative, but has occasionally clashed with, and annoyed, the establishment of his party. He is a loose cannon, whose temperament cannot be described as diplomatic. And, while he is well known, long present on the national scheme, quite witty, and highly popular in some demographic groups, he hardly shows the grasp of issues and good judgment required of the highest office.
His Democratic counterpart could then be a hero of the Civil Rights movement, reliably liberal but in frequent conflict with the Democratic establishment, a sometimes bad-tempered loose cannon, witty and popular with his base, but probably lacking in the grasp of issues and judgment... and someone like that actually did seek the Democratic nomination in the 1980s.
His name is Jesse Jackson.
Suppose Jesse Jackson had won the Democratic nomination in 1984. And suppose his first executive decision - choosing the running mate - turned out as follows. He chose someone complementing him demographically, an outsider unknown to most of the public, but with some enthusiastic followers. A person with some far-outside-the-mainstream ideas and beliefs, who calls himself a Democrat, but critical observers question that. A maverick who would not hesitate to challenge the "old boy network" in Washington, but who also doesn't have much respect for the law. Someone who will not blink in making decisions, but the prospect of him ever making decisions for the nation would scare the crap out of most prudent people...
Someone like... Lyndon LaRouche.
Forget about the utter implausibility of Jesse Jackson picking LaRouche to be his running mate. McCain picking Palin seemed just as crazy.
Would I vote for a Jackson-LaRouche ticket in 1984, running against the conservative visionary and orator Reagan, suspected by critics to be out of the mainstream, but able to inspire and connect with people across ideologies, and his running mate G. H. W. Bush, the experienced Washington insider with a moderate reputation and strong foreign policy credentials? Would I, first and foremost, vote against Reagan, whose ideology could not be farther from mine, and whom I considered a fake and a lightweight?
Hell no. As much as I disliked Reagan, I still required competency and wisdom of his challenger. Mondale had it. Gary Hart had it. (The Rice scandal didn't come until the next election, and as much as it warned of recklessness, it wasn't necessarily a deal breaker.) Jesse Jackson probably didn't have it. The hypothetical Jesse Jackson with a crazy VP pick like LaRouche would not have been even close to having it.
How many Democrats would vote for a ticket like Jackson-LaRouche? I bet considerably fewer than half. After all, look how poorly even decent, qualified candidates like Mondale and Dukakis did. Brand loyalty is much weaker among Democrats as it is; give them a bad candidate and they'll desert him without, um, blinking.
So no, we would not see this stubborn brand loyalty if the roles were reversed. What we see is that today's Republicans are an uncritical herd even by the notoriously low standards of political masses.