I would normally agree with you, but I think the ban is more about sending a message rather than eliminating the message Romney supporters push.
And the message being sent is, in part, this: as conservatives we are taking a stand once and for all against supporting RINO's foisted upon us by the establishment in the Republican Party. They are no longer welcome in this conservative circle because they relentlessly legislate away our liberty after obtaining our votes through bald faced lies.
I think of it this way: If I ever caught my wife cheating she'd be banned from my life, as in divorce. Free Republic has officially divorced itself from the RINO wing of the Republican Party.
Bingo!
The only message would be weakness and security. Can't conservative arguments hold their own against other ideas?