[Gianni]

I'm asking why the states, through a vote of their representatives in Congress, cannot expel another state?

A vote of their representatives in Congress would be a federal act, and thus must fall within the enumerated powers of the federal legislature.

And where is this Constitutional acid test that determines when action is 'necessary and proper' and when it is not?

The Constitutional acid test that determines when action is constitutionally derived currently lies with the Supreme Court via their usurpation of this power in Marbury v. Madison.

[Non-Sequitur]

A vote of their representatives in Congress would be a federal act, and thus must fall within the enumerated powers of the federal legislature.

Why? Is it not the states in Congress assembled? Do they not represent the will of the people of those states? Such a vote would still express the will of the states and, since not forbidden, should be able to expel Massachusetts. Shouldn't it?

The Constitutional acid test that determines when action is constitutionally derived currently lies with the Supreme Court via their usurpation of this power in Marbury v. Madison.

Where did the Marbury v Madison decision state that?