Kuiper disses Fortunov

F B J Kuiper says: "at least for those scholars who are agreed on
the untenability of Fortunatov's Law (which tried to account for Skt.
t.. d., n. by tracing them back to IE lt, ln) and the exaggerations
of the theory of the occurance of Prakritisms in the Rigveda"
--- Studia Indologica, Fs. fuer W. Kirfal, 1955; p 137-8

Is he allowed to say this? Won't they revoke his linguist's license
or something?

Seriously, is there even a significant minority of linguists who
doubt Fortunov's Law? What is their rationale?