I have made several mistakes in my thinking. Perhaps the arguments do not seem wrong, but that itself is irrelevant, for one does not need to be correct to seem correct; sufficient style is often able to make up for substance insufficient.
The key error is that my arguments follow from my position. If so, reason serves not to seek the truth, but to support whatever stand that has been chosen. This is not correct. Instead, the reverse method should be adopted, and a position decided based upon facts and reason.
To increase objectivity even for subjective affairs, I propose to first define a set of criteria by which one would be convinced or doubtful of a certain position. Often it is too easy to be mired in a debate where both sides have reasonable but not fully convincing arguments, where it is difficult to objectively and consistently weight both sides.