Only the market should be open source, and this is only to protect devs. They can release the software sort of like a proof of concept. Then anybody can take it and use it as they best see fit and assume all responsibility for their own legal or illegal actions.

If the market is closed source, than the devs can be held accountable, and at the very least, be obligated to remove the software but they can possibly even face legal consequences. They can be prosecuted as the operators of illegal activities and this is because in a closed source software the developers have control over what happens. This is not the case with a open source, as once the source is out in the open there is no way to control what the users will use it for.

If they release as open source they will renounce control but they also renounce any responsibility. If bitcoin had been released closed source then satoshi nakamoto would be in jail by now.