Blacklist all members from a server (avoid mass DM's)

So bots messaging people is something that's been going on forever, and I know this idea isn't perfect...  But why not allow server owners/mods to blacklist a specific server.  What I am envisioning is a server setting where you can enter a different servers ID (say one full of bots) and blacklist it, if a user is in that blacklisted server and they try to join, they will not be allowed to join directly to the server. 

With some quick Moderators on a fairly big server, this could help narrow down the amount of bots able to get in and message other users asking them to join these shady websites etc.  These server ID's could then be shared amongst other communities to help prevent bots flooding in.

Now of course there's the fact that some legitimate people might be in a blacklisted server and get aggravated at this, so maybe make something like a "request" with a message that can be sent so that people with the appropriate permissions may view these messages and decide whether to grant that user access or not. 

Obviously there will be a lot to iron out with this idea, so I appreciate your input below, but I haven't seen anyone else come up with an idea for a native Discord feature.