This is a typical argument of the type spread by experts in the marketing tactics known as "fear, uncertainty and doubt" (FUD) [about the competing product]. The "forking" argument was once commonly used by various "analysts" and the mainstream computer press to explain to the undecided why Linux is not worth their attention.
"Forking" in this context means "branching a computer program," so as to create parallel "subversions" of the program, and consequently fragment Linux and presumably reducing its usefulness.
There is very little (if any) evidence of harmful forking of any software included with a typical Linux distribution. Where forking did occur, it has always turned beneficial. Quite possibly, this is because although there are no artificial barriers to fork software under Linux, there are also no artificial barriers to merge the best pieces back.
The theoretical background on how forking software can be good for its development might have been actually given quite some time ago by the German philosopher Georg Wilhelm Friedrich Hegel (1770 -1831), with his concept of dialectic development. E.g., in "Phenomenology of Spirit", Hegel concludes: "... the schism incipient in a party, which seems a misfortune, expresses its fortune rather."[an error occurred while processing this directive]