If OneMarket will be opensource then the devs can not be held responsible for whatever the users do with the software, even if it is illegal stuff. Also remember that this is a world market and not all drugs are illegal everywhere so you can't push out of the market all the people who live in a more free environment than the western world.

Anonimity feature is a niche feature, and it is best suited for illegal activities. Say a user will not want to break any law then why would he chose cloak over bitcoin? There is no reason. Bitcoin is already being used successfully on the dark markets and in great volumes. Building Onemarket in such a way that only legal content can be sold will defeat the purpose of cloak coin.

Using private listings will create the need for third party sites that will list those adds in a searchable way also defeating the purpose of decentralization and not actually solving any problem.

The best way to make it work is to have OneJury as a option. If I am a user that is not interested in illegal stuff I will check OneJury option so that only reviewed listings will show in my results. If I wish to buy some drugs I will uncheck the option and all listings will show up in results.

Adding a listing should cost the same fee all over to prevent spam, but not all listings should be reviewed.