I think that an important principle of the American organization of power is accountability (that one which is "something left when responsibility is subtracted", according to a Scandinavian). I think that Supreme Court almost exclusively (meaningfully) interacts with the rest of the country via its decisions. I think that may mean that Supreme Court can be judged - and e.g. a justice impeached - solely on the basis of their decisions, as it's the only thing they do. Without this, I see a contradiction with the principle.
That means that if e.g. Congress finds some decisions of Supreme Court distorting Constitution, the Congress is justified in removing a justice solely on the basis of the decisions made by them.
