The fact that grid owners can technically ignore copyright law doesn't mean we shouldn't allow people to set restrictions on how their content can be legally used and try to enforce those restrictions whenever possible.
If we force merchants to give up all control of their content if they allow it to be exported from a grid then we are limiting the amount of content that will be transferable to only include freebies. What merchant that wants to sell content would agree to sell an item just once and then have it become public domain?
This type of forced freebie licensing in order to be able to move content between grids makes the Export permission close to useless.
Anyone copying something they shouldn't (because they don't have the permissions to do so) is breaking copyright law. Merchants should have the option to decide that they sell something to only one person and allow that person to take that item with them when they travel the metaverse without losing legal (and as much as possible technical) control over the content they created. Stating that an item won't be able to leave the grid unless the person who created it allows turning the item into public domain will hurt cross-grid sales.
This type of Export permission equals freebie logic doesn't go hand in hand with having a metaverse where people can take content they bought with them when they jump between grids.