I'll admit the reasoning has problems, I made it somewhat facetiously to show you should never underestimate our ability to rationalize. I have to say that your rebuttal works just as well as an argument that the Church should start crucifying people. That's the Way of the Cross.
But it does address your theological underpinnings,, ie the situation is not "objectively" sinful, sin is not part of the question, and the Magisterium is fully in accord with personal conscience if there is no sin.