valtam: When will humans learn that killing, right down to the very last bad guy, is still killing and only serves to fuel rage and the desire for revenge in others.
That'll happen some very short time after the Daleks arrive and everyone says... 'Blimey, we'd better work together to destroy this evil!'
And once we've all globally agreed thats a good plan, and set right down to it, some mullet brained nappy wearer somewhere in the world will say, 'whilst they're all looking skywards I'll just exact the revenge for the generations of lost forefathers I may have had by topping the neighbors cousins best mates father-in-law... who's to know it was me?'
The Daleks will spill the beans to the father-in-laws tribal bro's, and go back to their ships for a spot of techo-tea and a recharge. Leaving us humans to finish the job for them, by getting back into doing what we do best.... destroying each other in the name of making the world a better place (for who so-ever cometh after).