I would like to print fancy plastic cutlery sets or plastic glasses.
Is it safe to do it? Or bad for your health, if so, why?
Having performed a quick search through all the resources at the FDA Food Contact Substance resource, I cannot find PLA in any list except an occasional notification that a specific manufacturer has obtained approval for use in specific circumstances, with the notice that such notifications are only valid for that manufacturer and cannot be used to validate another use of a substance.
There are companies that have received approval for their specific formulation and use of PLA as a food contact substance. You may wish to discuss this further with your material supplier to find out if they have approved PLA product available.
Without specific product approval, though, PLA is not on the lists of generally recognized as safe, nor approved for food contact use.
Regulations in other countries may differ, so you may want to search the EU directives, for instance, to find out their opinion on PLA as an FCS.