Not to speak for lessdazed, but what I understood them to be saying is that when I argue against a proposition P solely by pointing to the consequences of believing P, I am implicitly asserting the truth of P. I would agree with that.

I would say further that it's best not to implicitly assert the truth of false propositions, given a choice.

It follows that it's better for me to say "P is false, and also has bad consequences" than to say "P has bad consequences."