Stuff happens even in the safest, most controlled environments  When we design processes we can try to define out all potential problems or balance the degree of safety required and our ability to recognize and react when something happens.

Excluding all inputs that might cause a problem would also exclude impressions, interactions and potential serendipity that can foster innovation. This is a path towards mediocrity. Agile frameworks stress the need for transparency (transparency is part of empirical models) because transparency is needed for effective collaboration and feedback.  Transparency will mean external ideas could encroach on your projects. Trying to ban outside ideas will do more harm than good; just make sure you are communicating well enough to raise an alarm when needed.