It's important for Sloan that the default setup remain that these options are all available to all class and community admins. This functionality was one of the biggest selling points/wins for the system at Sloan because it gave faculty the autonomy they needed to run their courses and gave communities that same flexibility, especially since many have non-MIT members. And, for the Manage Membership link, since any member can drop any membership, but not rejoin a closed group, it's important that the group admin be able to add people back in. The more groups you have, the more adminstrative burden is placed on the site wide admin to monitor, without any tools, the actions of users.
I don't understand exactly what you mean by your last question - can you provide an example or two of this in action?