Did you tried as below?
1. Create a Security Group as "Email Designer"
2. Next if you click on that you can see the list of options like licensing,Interface access,Action permission etc.
3. From that choose default permission , this is for what are the activities the user can do when they create a Asset.
4. In the Email choose the permission you want to apply (it can be View , Edit, Delete secuirty)
5. Then for the Campaigns , under the Asset creator you can ensure that Activate is not chosen (View ,Edit, Delete, Security ,Activate)
Hope it helps
Yes, I've done that. That's what I described in my question. The issue is there is no "Asset Permission" or "Action Permission" to enable or disable Send Email.
Also, although I've set the group not to have the ability to create a Campaign, I am still able to Disable an active campaign as a user just with that security group.
The Campaign which you can disable now is the campaign created by you , before you make this changes to the security group?