Devil's advocate..

[Angrboda]

Let me give it a shot.

1. You assume that value system A is as deeply ingrained and arbitrary as value system B.
2. Therefore, there is no way to determine which is more right.
3. Without such a determination, it'd be wrong to impose one system over another.

In argument no.3 you have given a condition for determining which is more "right" - the condition being, without a clear determination of which is more right, the right thing to do is not to impose one over other.

I gave no such condition. The condition you propose is a completely separate question from whether one system is more morally right than another. The only absolute moral law which I would acknowledge offhand is that might makes right. Furthermore, you cannot examine the value of one maxim in isolation from the whole.

Applying this at individual level, we can conclude that it'd be wrong to impose an arbitrary value system upon an individual. So, a political system that ensures that such an imposition won't occur would be more right. So, while the two systems maybe regarded as arbitrary at an individual level (they may not be, but that is a different discussion), at a political level, one comes out as a clear winner.

Since you haven't established this to begin with, and, it seems like a rather arbitrary chunk pulled from your own values, the rest does not in any sense follow. And while I would agree that political right and moral right are related, you can't simply juxtapose one upon the other and hope for it always to apply. There are additional factors in play. And finally, all political systems impose themselves arbitrarily on those who are governed, so there is no such unimposing system to turn to for relief; you have erected a utopian alternative which does not exist save for those places where anarchy rules, and not even then.