If an IPFS host is completely open, in time it will inevitably host undesirable or illegal content. If it is closed to only a restricted set of users, then it become much like a private server and that defeats the objective of IPFS. Thoughts?
There might be a misconception about what IPFS is. Nobody can tell your node what to host (except with some specific configurations or tools like ipfs-cluster). So you won’t knowingly host illegal material unless you ask for them.
To be clear, when a node “add” a file to IPFS, what it really does is advertising that it has a copy available for other nodes to fetch. No bit from the actual data is actually transferred to anyone until they ask for it.
NB: There is also a preliminary project to have maintain blacklists of hashes you might not want to receive or serve, should you request them by accident.