We disagree that the Constitution establishes a specific goal for the Electoral College's existence. The one thing that is clear is that there is no explanation of "why" the electoral college is in place present in the constitution, as opposed to having the election be a direct democracy, for example. The only thing it describes is the "what" the electoral college will do and the "how" it is to be selected. It is merely implied by the fact that the election of president is not done via direct democracy, but instead it is done by this select body of individuals.
You agree that the Electoral College exists because the founders did not want the president chosen by direct democracy.
From there, the question "Why didn't the founders want the president chosen by direct democracy?"
The answer to that question, which is what Hamilton describes in federalist 68 but is nowhere to be found in the Constitution itself, are the ends toward which the effort of creating the electoral college was directed.
In other words, the answer to the "why do we have an Electoral College anyway" question is the goal of the Electoral College.
Unfortunately, the Constitution does not answer that question. Federalist 68, however does it quite clearly and in such a way that a reasonable person living at the time of ratification could easily read the text of the Constitution and conclude that it was intended to achieve the goals described in Federalist 68.
This is evidenced by the fact that there was no disagreement with Federalist 68's claims about the electoral college.
From that position, I can easily conclude that the design found in the constitution, which you point out allows states to undermine that goal, is obviously flawed for exactly the reasons you describe: It allowed states free reign to undermine those goals.
