A minority of bitcoin spending is on illegal goods and services, and of all illegal goods and services being bought, a tiny minority of them are bought with bitcoin.
In light of recent events, I stumbled across this topic.
One thing that I'd like to add, which wasn't brought up here yet, is the following point:
who defines what is illegal?
Take for instance the current politics in Russia, where you aren't allowed to call a war, a war, or where holding up an empty paper sheet gets you arrested. Those things are illegal there, so therefore we shouldn't incentivize the use of free (freedom) money to allow protestors to receive donations and fight for information freedom, peace and democracy?
Since drugs were brought up: in some countries they're legal, in others they're not. Meaning the exact same activity (owning or selling them) may be illegal in one country and legal in another.
What I'm trying to say is: at first thought, it seems trivial that 'illegal things bad', 'legal things good', especially if you live in a country with semi-alright laws; but if you really think about, the definitions of legal and illegal activities are often very subjective and arbitrary. Lots of things we do on a daily basis (like expressing our thoughts freely) are actually illegal in some countries and you'd be outraged if I told you not to donate to people who fight for peace and freedom, because in their legislation it's not legal. There are lots of things all over the world that in their geographic and temporary location are illegal, but we all here would still consider 'good'.
Maybe you'd like not to see Bitcoin used for 'immoral' (instead of 'illegal') activities; which I would agree with, as opposed to referring to some random country's law. Besides the fact that morality is again a super subjective philosophical topic, it's physically impossible to create free, independent money and at the same time impose rules on its usage.
In my mind, by definition, the best money is the one that can be used anywhere, by anyone and for anything.
My final point (while already being mentioned) is that criminality has always existed and criminals always find a way to transact money. You could even argue that by using cryptocurrency, the criminals' lives are actually safer than if they met in person to exchange cash, as we can imagine how that often ends, if two armed criminals meet with a large bag of money.