This relates to Confluence 6.9 EAP released - read-only mode is coming!:
Can we assume that Confluence itself disables all ways to insert/edit a macro when in read-only mode so that developers do not need to explicitly prevent writes that might otherwise result from persisting macro configuration? To clarify, the macro in question does not write any data at runtime (except for logs eventually), but besides the implicit macro parameter storage, it may e.g. also persist data to an Active Objects table or external data store at configuration time.