I will write-in a candidate or vote 3rd party.
The BIGGEST reason I won't vote for him is that, if he is elected (which I doubt VERY much), he will, with a vengeance, punish the conservatives in the GOP.
The Republicans in Congress will be helpless, because they cannot oppose a President McCain without opposing the leadership of their own party.
Conservatism in the GOP will be beaten back and shoved in a closet for the duration of a McCain presidency.
With a Democrat POTUS, the conservative wing of the Republican party will be mobilized and energized.
Opposition from the Republicans in Congress can be mounted without going against their party leadership.
And McCain will be defeated, discredited, and powerless to interfere.
I submit that a Democrat president, even the communist crypto-Mahometan Obama, or the Shrieking Shrew sHrillary, would be far more likely to advance conservatism and conservative causes than a McCain presidency.
Regardless who wins (Hussein, Mrs. Filegate, or McCain), amnesty will be passed. With some 15 million new Democrat voters, the Dems have a guaranteed lock on the elections for a decade.
The best we can hope for is to become a loud-mouthed minority who they ignore.