They did. The piratebay default search engine allowed people to find illegal content. That's why they got in trouble. If Google Chrome default search engine had CP and drugs on it, they'd get into trouble too. Anyone can use chrome to find CP but Google is ok because they don't enable it by default. As long as OpenBazaar default search engine does not contain anything illegal and forces people to use a different search engine to find illegal stuff, they will not get into trouble.
I don't think you're able or willing to delist content right?
I mean, this is damning: Illegality and immorality are different, and - speaking personally - I don't have an issue with the platform used for moral but illegal uses.
It does not just matter that something CAN be used for evil, it matters how likely it WILL be used for evil.