I feel like you need to differentiate between paying with dollars online and irl. Of course the material dollar is harder to trace, but it's not like you can pay that way if you want to buy illegal stuff over the internet. If your choice for online payment is between a bank transfer and payment in cryptocurrency, then cryptocurrency is definitely safer and more anonymous. Nonetheless making argument against cryptocurrencies based on that is just silly to me. If it's not there, people will find another way around the problem anyway.