We can be certain that, if there are conflicting views in different cultures, some of these views must be false. This may help us to transcend our own narrow cultural horizon.
We own ourselves. This is the core of a libertarian theory of rights. But on this theory, while we are at liberty to kill ourselves (regardless of the consequences of others), we are not allowed to kill others, not even if this means that there we be fewer murders in the future, totally speaking.
According to deontology it is wrong to kill an innocent human being, period.
Different areas present us with possibilities to test different theories.
The US two party system is very different, of course. Here the people decides about who should rule them, but it is not reasonable to claim that the people rules itself through the political institutions. In comparison, I find that the standard European system is better, also as a model for global democracy.
