What do you call a person who will defend a point of view that she may not agree with not just for the sake of argument, but because the point of view is not represented in the argument?
Such a person is being objective perhaps? In the sense of being neutral and rational.
The phrase I would use would be defender of the underdog, which is an individual who defends people just because they need defending. It is different to devils advocate, which is an individual who adopts a position they may not agree with for the purposes of debate.
The Walter Block syndrome - defending the undefendable.
This is a question that needs to belong to the philosophy department because to arrive at an answer, you would need to get behind the philosophy.
In conventional English, the title of the book would have been "defending the indefensible".
It is libertarian jurisprudence fulfillment of free-market principles.
The principle behind such sentiment is that every known position, contentious or otherwise, must be defended as a matter of economic principle.
What you see as defensible (a steel manufacturer executive) might be working the system to his/her benefit - could be ethically right but morally wrong. Is the non-criminal executive a lesser criminal than the pimp? Why is a grocer allowed to go about his/her business, while a pimp cannot? You, in your frame of mind, of course has the answer - "What, a pimp vs a grocer? Isn't that a no-brainer?"
The Libertarian viewpoint is that his so-called "so-called authorities" (cascaded so-called intended) are making an economic offer that the offeree is not allowed to refuse
That such offers are against free-market principles. In a free market, you are allowed to refuse an economic offer of trade.
Therefore, a Walter Block disciple/sympathizer/adherent.