"And that comment... "a mere compilation of facts...." is part of the reason photography, especially documentary photography, gets so little respect among the art world."
I don't disagree that the argument doesn't hold water in the real world (or is it the art world?).
But it isn't art criticism, it is a legal argument. It deals with the legal meaning of phrases that have a legal context, and are the subject of many legal decisions.
I don't know, but think that I am safe in guessing, that there are cases where "mere compilations of facts" are not entitled to the protection of copyright. The legal argument being made is that Patrick Cariou's work is more like those "compilations" than original pieces of art.
When one makes legal arguments, one hopes to gain the benefit of any uncertainty there may be in the factual situation. In this case, clearly there wasn't any such uncertainty.