You're not forced to stay in the same context. Contexts can be used for batching similar tasks, if you so choose, but the context lists purely present you with the options of things you can choose to do at this point in time.
I don't really get what your problem is. GTD is made up of principles, not rules. You adapt the principles to suit your own life. If you don't need multiple contexts, don't use them. The point is really simple - write stuff down so you can keep your head clear and focus on the things that are important, and step back from the 'busy work' during the weekly review to think things through properly. It's common sense.