I think it will attract a lot of people who are wanting to deal in illegal drugs (and other, more dangerous illegal items) and become a marketplace for such. The difference here verses other illegal drug sites is that the bar for selling is much lower so it would be easy for law enforcement to conduct sting operations from people buying drugs on these sites
There is no signs of this yet. OpenBazaar developers made it clear it is meant for legitimate businesses and will be attractive because it has no fees. However they also said they can't control what will be done with it as it is also censorship free but they hope the code will be forked for illegitimate usages.