There are decency issues that have showed up on many threads that must be dealt with and having an Admin available for that is vital IMO.
Apart from that, your idea seems okay. Zeev's politics thread has been managed effectively by Zeev and we have had a wide open discussion from all sides of the political spectrum without anyone going so far as to cause a major problem.
It's in the nature of political discussion to have debates and the debates can be heated without being uncivil.
And there's always the ignore function which has served me very well.