I hear you, but I believe it's a very strange and unstable definition. When you say that you want AI that "optimizes X", you implicitly want X to be optimized is a way in which you'd want it optimized, understood in the way you want it understood, etc. Failing to also specify your whole morality as interpreter for "optimize X" will result in all sorts of unintended consequences, making any such formal specification unrelated to the subject matter that you intuitively wanted to discuss by introducing the "optimize X" statement.

In the context of superintelligent AI, this means that you effectively have to start with a full (not-just-putatively-)FAI and then make a wish. But what should FAI do with your wish, in terms of its decisions, in terms of what it does with the world? Most likely, completely disregard the wish. This is the reason there are no purple button FAIs.