I understand what you're saying and from a "moral" perspective, somewhat agree. However, given the choice of, for example, 3 candidates:
1 - I disagree with 90% of the time
2 - I disagree with 50% of the time
3 - I agree with 90% of the time.
If #3 has no chance in hell of winning, I'm voting for the second one.
I've been down the road of voting for a 3rd party candidate and concluded I really was helping the guy I hated the most win. It turned out no matter how much I said, "but I voted for #3", I still had to deal with that 90% crap.
Having to live with that reality ended up trumping my pride and ego.