crime, organized crime at least, usually has profit motive attached (ignore terrorism for the sake of this argument). bitcoin is money, not quite anonymous, but anonymous enough at this point. the government basically doesnt like illicit earnings because it does not get to tax said earnings. whats one f the easiest ways to avoid taxation at the moment, with a significant amount of value?
bitcoin
so bitcoin will always attract the not so noble crowd, in its current form it just happens to be a pretty effective tool for transmitting illicit funds quickly and quietly
i think we are seeing more and more everyday that BTC is not ideal for illicit activity. it's easily traceable. a few years ago, blockchain/taint analysis wasn't a big thing, but there is an entire industry based around it now. and these companies work very closely with law enforcement agencies. in that vein, it's no big surprise to see alphabay and hansa shut down the way they were. i would even be wary of some of the BTC mixers..... if i were the FBI or INTERPOL, i'd be running mixers as honeypots. hell, law enforcement was running hansa as a honeypot!
i hope that XMR continues to confound blockchain analysis companies. it seems to be our best hope for anonymity of the blockchain.