During Draupadi's marriage, there was a dilemma regarding whether five brothers can marry a single bride. Draupadi's father, King Drupada, and her brother were all against it, quite naturally. In this context, Yudhisthira said - (Mahabharata, Adi Parva, Vaivahika Parva, Section 198)
'My tongue never uttereth an untruth and my heart never inclineth to what is sinful. When my heart approveth of it, it can never be sinful.'
My question is not about why all Pandava brothers married Draupadi.
I am concerned with the specific logic that Yudhisthira offered. In my humble opinion, if society accepts this kind of logic, it won't take much time when everything will fall apart. For example, imagine a terrorist is justifying his terror by saying, "I think it is dharma, so it is dharma."
How come a person becomes the authority? Is Yudhisthira above Vedas and Smritis (social rules based on the Vedas, as far as I know)? Or is this kind of attitude approved in the Vedas, Smritis itself? Is there any such provision, which says whatever you think is dharma? Can somebody give any reference from authoritative texts which supports this kind of statement?