为什么像RedirectToAction（）和HttpNotFound（）这样的Controller方法受到内部保护？

I want to implement a service pattern to provide some logic for several of my ASP.NET MVC controllers. Depending on the result of the logic, I may want the controllers to redirect, or give a 404 not found, or various other responses. Therefore I want my controllers to be able to receive an I want to implement a service pattern to provid