“We can’t know what would have happened if $historicalfigure hadn’t done $badthing,” is a very weak line of argument. One could similarly suggest that the Nazi Holocaust was better than what might have happened under other circumstances.
If you actually want to argue that the Holocaust was the better alternative, I'd be interested to hear your case on what that alternative was.
There's a reason that Kissinger was afraid of too much reliance on data, and that's why. As a German Jew, Kissinger experienced the start of the Holocaust. I imagine he's more adept at distinguishing bad from worse than either of us are.