Reason for forbidding: Time is not a straight line. There are many parallel timelines, many of which have things that should not be awoken.
Reason for forbidding: Even at its weakest, Rulecraft focuses on rewriting the laws of reality at a localized level. Larger-scale rituals can completely undermine standardized logical constructs.
Reason for forbidding: Combat alchemists are extremely dangerous figures, capable even of transforming opponents at a distance. The amount of magical energy required to do so permanently is monumental, but even temporary use can easily kill. Monetary use is strictly controlled.
Reason for forbidding: Fate is elusive at best, and not understood well enough to make changes safely. By interfering too much with Her design, entire worldlines have been destroyed.
Reason for forbidding : Suborning the will of another is one of the greatest taboos.