I don't understand why the cult should even cause revolt if you try to keep it out. I mean, not letting in a cult that is babbling about nonsense for all your people are concerned should not make them produce absolutly nothing for a while. If anything i would suggest that it simply causes temporary unhappiness or better yet, have one option that keeps it out and cause unhappiness, one option that lets it in, and another option that makes the cult less likely to spread into that city and to a lesser extent your entire civ, but causes revolt. That way, you can choose to continue with what you are doing now and risk it coming back, or have it mess you up a lot now but make it less likely that you will be hurt when you are doing something more important