The only trail it leaves is to financial institutions (who can see the transactions), and the government. The former need to be held accountable by law, by the latter. I believe the GDPR may aid us there.

Now, in a free society, I don't see a good reason why one should be afraid the government can snoop around my financial transactions. I believe I currently live in such a free society. If I want, I can buy a dildo or latex costume in an Amsterdam sex shop within an hour tomorrow, and I am not going to have to be shy about that. I don't live in a country where, for example, gay people get beaten up regularly. I'm not gay myself, btw, but I've experimented a fair share with my sexuality when I was younger. I also used to buy legal drugs online, and I just paid by IBAN. Do I want my employer to know such? Well, I'd like to have the choice to do so, and I have this choice as it is.

I can think of some very good reasons to use cryptocurrency in my free country, and none of these are valid from a legal PoV (avoiding taxation, buy illegal drugs/weapons/etc ie. criminal behaviour). By using cryptocurrency where other means work perfectly fine, I add noise to the cryptocurrency data, and it isn't in my interest to add this noise as I am not a proponent of things such as avoiding taxation or criminal behaviour.

Furthermore, nothing what you say addresses the other points:

> Cryptocurrencies have a tendency to be abused for speculation, and are bad for the environment.

These cons still exist, and need to be put on the weight with the privacy aspect. Which can be a valid argument in an unfree society, such as for example Belarus or China.