The Monroe Doctrine was nothing but useless posturing that was later used as justification for American imperialism in Latin America.
Minifidel,
Close, but not quite.
The policy that became the Monroe Doctrine was actually first saw life as a British diplomatic proposal. Santander, Bolivar, and the rest were busy removing Spain from the American mainland and Britain was worried about those Spanish colonies becoming colonies of some other, more capable, European power. (The parallels between this and the Philippines in the 1890s is striking.)
Accordingly, Britain approached the US about a joint declaration. Monroe, sensitive to the potentially grave domestic political issue of working with Great Britain so soon after two wars with that nation, decided that the US should issue the policy in it's own. John Quincy Adams drafted it, Monroe presented it during a State of the Union address, and Britain saw no need to make a statement of it's own.
This method in which the doctrine was announced gave each the US and Britain "plausible deniability". The US was following a British diplomatic lead without being seen as doing such and Britain, who would be enforcing the Doctrine for the first 75 years, would have made no official statement on the issue whatsoever.
As the sneering contempt for the Doctrine in your post nicely illustrates, the policy is viewed with suspicion in Latin America. That wasn't always the case however. Independence leaders from Mexico to your Argentina hailed it, seeing it as political hedge against European reconquest and knowing full well that Britain was the true power in the equation. Bolivar himself even lauded it during the Congress of Panama.
From a Latin American perspective, the trouble began as the US grew more powerful and presidents after Monroe began adding different interpretations to the policy. Very early on, the US invoked the Doctrine over treaties between an independent Texas and Britain. While the Doctrine originally dealt only with new colonies, Grant expanded it to include the transfer of colonies, Cleveland expanded it to include border disputes, and Teddy Roosevelt - who else? - put the Doctrine in the form that Latin America now loathes.
As an aside, the US played nearly no part in the actual enforcement of the doctrine, since it was all done by the British anyway (as has already been mentioned). So, no Monroe Doctrine... nothing changes.
Again, not quite.
The US began "enforcing" the Doctrine as early as 1866 when Johnson invoked it against the French in Mexico. Britain hadn't taken up the Doctrine in that case because she had been part of the original seizure of Veracruz for loan payments that France had piggybacked her actual invasion on. Cleveland, by the 1880s IIRC, had announced his border dispute addition. US enforcement of the Doctrine began within ~40 years of Monroe's speech.
If Monroe hadn't announced the Doctrine, Britain most certainly would have announced the same policy on her own. There wouldn't have been a "Monroe Doctrine" in that case, but there would have been something almost exactly like it. Also as the US' power and influence grew, some later president would have announced something similar too.
Then Latin America would have
two Doctrines to complain about!
Bill