In the same way, other currencies don't fund terrorism.
People are the ones who fund terrorism and would any means necessary in order to send the money across. Before the discovery of cryptocurrencies, terrorism has always been funded using various means most especially, the most used form of payment, the fiat system.
Cryptocurrencies is one of various medium of exchange and financiers of terrorism could use this, as well as any other method to get their funds across and finally in the hands of terrorist.
People against bitcoin and cryptocurrencies would want to lay all the fault at the feet of cryptocurrencies for solely being the means by which terrorism is funded.