Lots of people think he's angling for HomeSec in a Boris Johnson government. Which he likely is.
I actually think it's sorta legit, too. IDS has always been one of those moralizing, neo-Victorian types, who actually does have something of a moral sense...his economic understanding of how to solve the issues of poverty are terrible and bound up in a whole bunch of moral nonsense, but he does actually have some basic human compassion and despite completely fucking it up, he does want to help people. He's not alone, even on the right, in thinking these cuts are completely unjustifiable.
He may also be thinking long term. Going this hard, against a group which, as he admitted, "don't vote Tory" will provoke a backlash. Just imagine if, say, a PM Corbyn used the complete lack of empathy on display here to justify similar punitive measures against core Tory demographics. Even in politics, there are unspoken rules and recognised red lines. One can certainly punish and whip the other side's supporters to a degree...but without limits, the whole thing falls apart.