Its a simplification, and not a very incorrect one. The purpose of Fair Use is to reserve for society those uses that benefit society more then they hurt copyright owners. Whether a use is "necessary", while not a legal definition, is a pretty good rule of thumb for some possible Fair Use defenses.

ETA: also this is completely ignoring any relevant international laws. French law, which is where the OP lives, appears to provide some protections for "necessary" use.

"The Court of Appeal disagreed and applied French law. Nevertheless, it too rejected plaintiff's claim and decided that Google benefited from the "safe harbor" provisions of the Loi sur la Confiance dans l'Economie Numérique [the relevant French statute]. It considered Google as being a "neutral" actor and the reproduction of the photos necessary to provide the service."

http://cyberlaw.stanford.edu/blog/2011/01/who-said-france-do...

Yes. It's a simplification.

Necessity isn't a criterion for fair use, it's the reason fair use provisions exist in the first place.

Making satire of or discussing a copyrighted work without using copyrighted material is extremely awkward if at all possible. Internationally speaking (i.e. aside from the specific definition of fair use in US law), necessity is a good rule of thumb, just like profit/non-profit use.