Old thread but in case anyone digs in here, to see the security_admin role, you must have the security_admin role. If you already have the security_admin role assigned to yourself, you must activate it by clicking on your user icon and selecting Elevate Role. From the next screen, check the box next to security_admin. Now that you have that role, you can see it in the role slushbucket for users, etc. Note to that if you are trying to add a user to a group that has the security_admin role assigned to it, the platform will kick the user back out of the group if you don't have the security_admin role elevated for yourself. I've made this mistake many times. I believe in Utah or Tokyo SN added better error handling on this and now throws an error when this happens.
