membership plugin: invalid access

I setup 2 categories: Premium and General
I created a level called "Free Users" and added the "General" category to the "Positive Rules".
I created a post in the "Premium" category.
I created a user and manually added the user to the "Free Users" membership level (but didn't add a subscription)
I logged out and tried to browse the post and it redirected me to the "no access" page.. Great!
But when I logged in as my "free user: I was able to see the content.

This plugin is FRUSTRATING me! lol

p.s. Why are there both positive and negative rules anyway? Why not just add stuff they have access to and don't add stuff they don't have access to? Maybe I just don't get it.