Leaving aside the awesome stuff and stuff that makes me personally happy (I laughed out loud at footnote 1), Scalia puts the critical issue succinctly when he writes that those who fear unelected bureaucrats interpreting the law make no improvement by shifting the interpretation of the laws to unelected and even less accountable judges.
This is the real core philosophical difference between conservative jurists who genuinely despise "judicial activism" and those who simply despise it when liberal judges exercise the prerogatives of conservative judges. The dissent is all about how awful big government is and the essential role of the judiciary to reign it in. The majority opinion by Scalia is that this is poppycock. Congress is the legislative body. If it wants to "rein in" the exercise of "big government," it should pass laws to that effect. Where Congress deliberately delegates broad authority to the executive, that delegation must be respected by the judiciary.