Dan Bull’s work is a parody and criticism of Lord Finesse.

[i]n truth, in literature, in science and in art, there are, and can be, few, if any, things, which in an abstract sense, are strictly new and original throughout. Every book in literature, science and art, borrows, and must necessarily borrow, and use much which was well known and used before.

The germ of parody lies in the definition of the Greek parodeia, quoted in Judge Nelson’s Court of Appeals dissent, as “a song sung alongside another.” 972 F. 2d, at 1440, quoting 7 Encyclopedia Britannica 768 (15th ed. 1975). Modern dictionaries accordingly describe a parody as a “literary or artistic work that imitates the characteristic style of an author or a work for comic effect or ridicule,” or as a “composition in prose or verse in which the characteristic turns of thought and phrase in an author or class of authors are imitated in such a way as to make them appear ridiculous.”

…

[A]s to parody pure and simple, it is more likely that the new work will not affect the market for the original in a way cognizable under this [market harm] factor, that is, by acting as a substitute for it (“supersed[ing] [its] objects”). See Leval 1125; Patry & Perlmutter 692, 697-698. This is so because the parody and the original usually serve different market functions. Bisceglia, ASCAP, Copyright Law Symposium, No. 34, at 23.

We do not, of course, suggest that a parody may not harm the market at all, but when a lethal parody, like a scathing theater review, kills demand for the original, it does not produce a harm cognizable under the Copyright Act. Because “parody may quite legitimately aim at garroting the original, destroying it commercially as well as artistically,” B. Kaplan, An Unhurried View of Copyright 69 (1967), the role of the courts is to distinguish between “[b]iting criticism [that merely] suppresses demand [and] copyright infringement[, which] usurps it.” … Of course, the only harm to derivatives that need concern us, as discussed above, is the harm of market substitution. The fact that a parody may impair the market for derivative uses by the very effectiveness of its critical commentary is no more relevant under copyright than the like threat to the original market.

Campbell v. Acuff-Rose Music, Inc., 510 U.S. 569, 575-93 (1994) (all brackets in original).

The point Dan Bull is trying to make is that it is ridiculous and hypocritical for Lord Finesse to sue someone for using his beats in a free song when (1) it’s a widely accepted norm within the rap industry to reuse others’ beats without credit or payment and (2) Lord Finesse has done exactly what he’s suing Mac Miller for. Using Lord Finesse’s beat to do it is essential to making the point.

As for any argument that Dan Bull’s work will destroy the market for the original, well… even if it’s true, too bad. That’s what happens when you piss off your potential customers in a free market.