(1) the purpose and character of the use, including whether such use is of a commercial nature or is for nonprofit educational purposes;
(2) the nature of the copyrighted work;
(3) the amount and substantiality of the portion used in relation to the copyrighted work as a whole; and
(4) the effect of the use upon the potential market for or value of the copyrighted work."
-- 17 U.S. Code § 107 (https://www.law.cornell.edu/uscode/text/17/107)
I don't know how one can read this as an impartial observer and make an honest argument that OpenAI is in the right.
Their use of copyrighted material does not fit any of the purposes enumerated in the first paragraph; it fails criteria #1 because it is of a commercial nature; it fails criteria #2 because it includes all kinds of works; it fails criteria #3 because it's not limited to very small extracts; and it fails at criteria #4 because their products are already having an obvious effect on the market.