There is a kind of reasoning that is often heard, where the irreality of some abstraction is inferred from the fact that entities that fall under it are not perfectly homogenous.
(1) A lot of times one will hear this at the beginning of talks about some academic subject. E.g.: "I am invited to talk about Penguins. But there really is no such thing as Penguins. There are Aptenodytes, Eudyptula, etc. ..."
(2) At other times one will hear such argument in political debate, often where the abstraction in question denotes a group whose political agency is disputed. E.g.: "There is no such thing as Islam, there are sunni, shia, ...", "There is no such thing as the French, there are alsacians, brittanians, ..."
(3) Sometimes in more philosophical contexts one might even hear something along the lines of: "Every stone is different, therefore there is no such thing as 'stones'." This form seems to be taking (1) and (2) to their logical conclusion.
While the conclusion of these arguments might be a perfectly valid position regarding the problem of universals, the argument itself seems blatantly fallacious. The concepts of Penguins, Islam, French, stones are partial abstractions and do not imply perfect homogeneity, nor does the fact that they have identifiable subclasses characterized by relevant properties imply that their general abstraction is useless, meaningless, or "fictional", as is sometimes claimed.
i have seen this kind of argument so much that i wonder if there is an established name for it, or if there is some historic philosophical debate in which it featured prominently.