ok, so you originally mention human decency, then you talk of what can stop abuses of human rights. It is obvious that certain types of people are drawn to power, and will abuse others rights to maintain their power. These people are not decent. The only way to enforce decency on those in power is to limit the rights of the government in regards to how it treats its governed. When the government reports to the people, as in the faded piece of parchment, then the people have a chance of forcing decency upon those in power. When the govenment decides that the people dont need to be informed, and that they should just leave the decisions to the grown ups, then even if they currentlhy arent being abusive and indecent, they have set the stage for someone who will be a complete shit and crack down on everyone they can.
I dont see the circular problems in my statement. the laws are descended from an original source. If you choose to dismiss any and all value from that source, then that is fine, but dont just expect anyone with any shred of power to be decent to you on their own will. This goes from the POTUS to the board of a neighborhood association.