I do NOT think politicians should lie, just like I don't think spouses should cheat, but I do think that you will find it difficult to come up with the names of very many statesmen or stateswomen at the international level who have been very successful and who haven't committed their share of dissimulation.  Can you?  (I can think of a few possible candidates off hand -- Dag Hammarskjöld and the Catholic Popes since John XXIII -- but their exception appears to prove the rule by their extra-ordinariness, doesn't it? And their success seems somewhat limited compared to other good statesmen who haven't been so pure.) Maybe some sins are more forgivable than others, so perhaps we can expand our criteria beyond obvious and useless cliches.