Yes it’s very dangerous that’s why only these new-age folks on LD4all and other hippies practice LDing. ( :P)
You don’t control everything, not even [the events] during a lucid dream. The only thing which changes is that you know it’s a dream so it becomes like waking life, but there are stil factors which you do not control: environment, other DCs, events. (Yes it is possible to control these but very few people would want to control everything in a dream).
For internal control: You have an autonomic nervous system which you don’t control (when you drop a pencil and try to find it, this helps you [in doing so], because else you would fall over or be unable to find the pencil). Also, IWL you don’t control external factors at all, it’s not like we have the ability to make everything happen the way we want it…
Besides… what would be the problem with being capable of conciously regulating all internal and external processes? It’s true that the brains’ increased activity causes an increased crave for glucose, but since this is purely hypothetical: such a thing wouldn’t happen.