I don't think 100% anonymity is possible.
It's possible to reach 99% anonymity by either using self-mined blocks or cracked insecure private keys, operating from a public toilet seat in a crowded environment using their non-mandatory-registration wifi connection with a MAC address changed client booted from a live OS distribution, finally chaining the proxies after the wifi entry point.
Sometimes, you can legally crack private keys and take all the funds by solving puzzles.
If you're seeking for legal anonymous coins to crack, follow this internal link. That's your chance 
I don't need 99% anonymity. This is why my best practice is to do the buying&selling through face-to-face meetings, then paying my VPN using VPN prior to every expiration, which still sustains me good amount of anonymity.
it would be very simple if you never exchange your coins, for dirty fiat money, even if they could track back you, address by address...
then how they can say that those addresses belong to you if you didn't use them to purchase anything and therefore your name does not appear to be connected with any of them? impossible
If the govs thinks that it's relevant, they'll just do a house search which is displeasing enough for making efforts avoiding. Some countries also have mandatory password disclosure laws which brings you in danger by possibly finding illegal data by chance after decrypting your storage. For example, you could get in big trouble if you possess data which was perfectly legal when you acquired it but was being outlawed by the govs after some laws got tightend, possibly leaving you in possession of illegal data without even knowing.