Many topics in politics have no right or wrong answer and are purely subjective. Just two opposing and irreconcilable differences in philosophy.
For example, whether or not capital punishment is acceptable. That is purely an opinion of philosophy, there is no hard mathematical answer.
M: Perhaps you would consider what you just said here as an example of pure subjectivity. I can agree that is certain matters where law stipulated definitions, at what age a person may drink alcohol, vote, join the military, etc, the years required are matters of subjectivity based on general experience. But even here, some science averaged appeal to reality is implied. It is always older people looking in retrospect that set these ages from their experiences with living. They may be relatively subjective, but not absolutely so.
No, I think that what happens between two major lines of reaction to life we call conservative and liberal is that the irreconcilability that exists exists in everything including philosophy and an argument for objective truth can even be pushed there. Some philosophies are better or worse than others and that these differences can and are tested where the irreconcilable differences then move on to argument over the validity of the tests, as we see in global warming.
But we can all I think objectively agree that the global temperature is increasing, decreasing, or staying the same, and humanity is or is not having any influence on this. In short, it seems to me that the things that folk argue about are either right or wrong or irrelevant and that real and better understanding can be derived by testing.
What you leave out of your analysis, I think, is the business of motivation, that what is truth and what is lie depends on what skin you have in the game. Every bigot is a bigot, in my opinion, because at his core he feels his bigotry is good. It is not his opinions that he defends, but the feeling that he has to be right or the good will suffer. The average person, it seems to me, wants to be on the side of good and not on the side of evil. You are not going to just walk up and knock somebody off his white horse.
So the enemy of objectivity, it seems to me, is that folk have dominant concealed prejudices, they do not consciously know why what they feel is good IS good and they can't look at that if it could mean that good turns bad. This unconscious feeling that good will turn to bad if they are wrong is why people will not see.
A saying I love is this:
"You can always tell a bigot, but you can't tell him much." I just explained why I think this is. But this also tells us that people who are not bigoted in the same way that the bigot is can see his bigotry.
The bigotry of the South, also found in the North, that black people were inferior, perpetuated the institution of slavery. Slavery was destructive of untold lives, black and white also. I believe it to be an objective fact that black people are better off free and so is American society. Thus I believe it is also an objective fact that humanity free of bigotry is better than humanity infected with it. Thus our little political differences of subjective opinion, as you call them, make a huge difference in whether humanity is better off or not.
For these reasons, I believe the truth matters, that there is a truth, and that to know what it is requires freedom from bigotry.
In short, the little discussions we have here on this forum are actually part of an ancient war between light and darkness that one can perceive externally or internally with the same stakes, the survival and evolution or extinction of the human race. Thus, for me, the truth matters. But while it may matter to me there is nothing I can do but say what I think. I can't make anybody who wishes to be blind see. The blind are blind because they can't see they wish to be.