It seems a market has to fall under at least one of the following:
1) Scammed users by shutting down the site and taking user's funds.
2) Practiced improper security and put their users and themselves at risk.
3) Blatantly lied to users in a way which could put them at risk.
4) Got hacked and were unable to recover.
Depending on what you believe, anywhere from 1 to 3 are applicable for Silk Road.
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