Exactly! Well put. It is like saying it is legal to steal from a convenience store because hundreds of people shop there every week.
It isn't the act of executive order that is being disputed. The EO has to be pinned to some leeway given the president by congress in a law, or with regard to the administration of the executive branch. When you start talking, as Obama has, of using executive order in lieu of laws passed by congress he is expressly over stepping the EO authority.