How will Lemmy handle illegal content like drug dealing, child porn, snuff movies etc? On Reddit, the corporation is accountable so they will make an effort to ensure non of this exists on their platform. And they would face legal troubles if they failed to act.
But as Lemmy is decentralised this isn’t really possible. Sure the main instances can defederate from bad instances, but those instances could still operate and be accessible on the web. Especially if they’re hosted in countries outside of the western sphere of influence. Multiple bad instances could federate and duplicate the illegal content pretty easily, making it difficult for the authorities to keep it shut down. Has this been thought about already?
The open source nature has nothing to do with it, only location and type of content. Depending on your county’s laws the entity hosting the instance that has the illegal content might be on the hook, and the uploader is definitely in legal trouble.