I would probably say that any sphere can be used for good or evil, but that channeling magic from any sphere throws off one's inner balance between the elements and causes one's personality to change to be more like the god who presides over that sphere. It is also much more difficult to channel a type of mana that is not already dominant in one's psyche. It takes considerably more strength of will to use magic in a way of which the god of that sphere would disapprove, as the act of channeling would bring your desires closer to that of the god and destroy your resolve to keep casting in that manner. Mastering Trust of Foresight is probably possible, but the mage would likely be mastered by Deception or Greed before that is complete. Power relationships are a 2 way street, and it is hard to tell whether one is using or being used by his power. One can never completely master a sphere without becoming the god of said sphere, but becoming a god means loosing one;s free will entirely to the precept.