Probably they never heard about this universally accepted principle:
“You can never justify one wrong with another wrong.”
If they were principled they should have said " we want to impeach and try Musharraf and also try all those who ever abrogated the constitution"…instead of “we want to impeach and try Musharraf only if all those who ever abrogated the constitution are also tried…”
But then talking about MQM and principles…double nuff…