"If you don't vote for Obama, you're helping elect McCain" is not an absolute truth. Please stop saying it like it is.
When you assert that a failure to support Obama is de facto support for McCain as unqualified fact, you are engaging in the discussion as if every American lives in a swing state, the electoral college doesn't exist, and the presidency is decided by a national popular vote total. All of which are wrong.
Very few of us are going to be casting votes that have the potential to determine the outcome of the election.
Many of us can vote for neither of the two major party candidates without helping or hurting either one. And the rest of us, who do live in swing states, can engage in strategic vote exchanges.
Your failure to acknowledge these realities makes your entire argument intellectually dishonest.
So please, do us all a favor and just. stop.
Thank you and have a nice day.