No he's not.
As I said in another comment, as far as I know, as long as they don't host any nodes with illegal content, they shouldn't get in trouble just for publishing the protocol, the client protocol and p2p servers code. Otherwise, the inventors of tcp/ip, http, bittorrent, telnet and more would be in prison. And no, just saying "I'm ok with people using it for evil" is not a reason to go to jail, 1st amendment comes into play here. Now, if they start relaying nodes with CP on it, even by accident, that's a difference story of course. My guess is that their software comes with only their safe node on it and people will use search engines to get nodes addresses with CP on them. If anything, this will give more work and trouble to Google, not OpenBazaar.
Yeah, he’s going to prison, but that doesn’t mean he’s wrong about the potential value of his platform, and it doesn’t mean his motives aren’t good. It probably does mean that idealism is a shitty defense in court though.