One role that fits your description is lawyer. That category of person is routinely called upon (and answers the call) to argue differing points of view, some of which are wholly inconsistent.
They also regularly take multiple, sometimes contradictory, positions within the same legal brief, referred to as "arguing in the alternative" in which they are, in effect saying,
If you don't accept that explanation, what about x [an alternate explanation]?
They are often called advocates because they advocate for a client's point of view, regardless of their own position or belief (or the position or belief of one of their other clients).
If the person lacks admission to the bar, you might just call them inconsistent.