I don't like people to look into my pockets and Bitcoin allows that too easy. Mixers fix that. Monero also fixes that. Is that illegal, I don't feel so.
Not at the moment, but I can see a future where it is. Governments the world over are prying more and more in to the lives of their citizens. Wikileaks, Snowden, etc. have shown the world that mass surveillance is commonplace. William Barr and other high ranking officials keep pressuring companies like Facebook to build backdoors in to WhatsApp and similar apps to allow the government to snoop on encrypted messages. Governments regularly request data from Google, Apple, Microsoft, health insurance companies, etc., who hand it over in the vast majority of cases. Surveillance states are growing in both number and reach, and it won't be long before governments start using blockchain analysis to ascertain exactly how much bitcoin everyone is holding, if they haven't started already.
All in all, wasn't also Bitcoin "advertised" by media as drug money and so on? But time has shown that they are wrong.
I've always been a fan of Andreas Antonopoulos' response to the argument that bitcoin is used to buy drugs, which is essentially along these lines: Drugs are the second most traded commodity in the world, after food. The entire definition of money is that it can be traded for goods and services. If you can't buy the second most widely traded good in the world, then what you have isn't actually money.