I am not a purist. There is no such thing as a perfect political party, or a president who governs in accordance with one's every ethical judgment. But some actions are so ruinous to human rights, so destructive of the Constitution, and so contrary to basic morals that they are disqualifying. Most of you will go that far with me. If two candidates favored a return to slavery, or wanted to stone adulterers, you wouldn't cast your ballot for the one with the better position on health care.
I used to say that at least Americans' belief in the Constitution ensures that they will fight for the rights outlined in the Bill of Rights. The Constitution should protect us from tyrannical government actions such as capturing people and holding them without charging them with a crime (and giving them a fair trial), such as unwarranted surveillance, and such as extra-judicial executions through a secret committee that selects supposed enemy combatants for assassination. But the Constitution can only protect us against these things if we insist that it do so.
I want to like Obama. I read his book and endorsed him because he seemed like a smart guy who could get the job done. And he supposedly was going to put a stop to the unconstitutional actions and human rights abuses of the previous administration. But by being the bi-partisan compromise guy on issues like torture, he creates strong unconstitutional precedents that will now be very difficult to ever roll back.
On the other hand, the main thing I learned from my foray into Naderism (and its GWB consequence) is that -- no matter how bad things are -- they can actually get unimaginably worse. There isn't really a rock bottom to hit where we can reasonably say "we can't go any lower than this" until our species is actually extinct.
So I'm not sure I want to encourage protest votes or abstaining from voting because God only knows what might happen next...