So by your warped view, our Constitution is therefore illegal.
Let's put it this way, it was beyond legal. The Congress didn't know what to do with it, so they passed it along to the states. The states held their conventions. In effect, it was a revolution, as Patrick Henry described it:
Here is a revolution as radical as that which separated us from Great Britain.
And so, it came to pass. That doesn't mean we have to live with the mistakes of our forefather for eternity. At some point, we ought to correct the errors.