Group and Spaces module are identical to WhatsApp group system where you either allow every member to post or limit it to only Admins - this was fine as members were drawn by you from your phone contact. (Problem started on WhatsApp since joining from web pages were made possible - you can join any WhatsApp group, post rubbish and exit the group)

In UNA there is also a challenge because it's web based and a public Group doesn't have the preliminary need for a member to already exists on your phone contact. So a public Group can be joined by anybody anytime once they are already a member of your website.

Since many CAUSE or INTEREST or ADVOCACY GROUPS will be having public status, there is need for Admin to be able to moderate posts before it's made public.

Otherwise the present design is ONLY adequate for MICRO GROUPS and SPACES that requires membership by invitation or confirmation IE members are already screened. Prescreened membership only work for Small Project Groups that are open to identified category of people.

Open social group and spaces needs moderation. Facebook has this feature.