This doesn't seem to me to mean as much as the author thinks.
By the same reasoning, after all, email as a communication mechanism is "dominated by" spam, much of it similarly shady in nature.
There is an interesting difference, though -- while spam actively hurts the usability of email, botnet traffic which parasites on the TOR network helps make the system as a whole stronger, by adding more noise in which the important uses of TOR can be lost.
By the same reasoning, after all, email as a communication mechanism is "dominated by" spam, much of it similarly shady in nature.
There is an interesting difference, though -- while spam actively hurts the usability of email, botnet traffic which parasites on the TOR network helps make the system as a whole stronger, by adding more noise in which the important uses of TOR can be lost.