Or those good conservative, capitalist aliens might really be saying, if Humanity doesn't get that plague of liberalism under control we must destroy earth to prevent it's taint from spreading into the rest of the galaxy. They learned many millennium ago that liberalism is the greatest threat to galactic prosperity... (Hey my stupid, totally baseless theory is just as valid as their stupid, totally baseless theory)
It is typical of the liberal mindset to think that aliens would automatically agree with them when your theory would be more likely that liberalism itself would more probably be viewed as a disease (people who murder their unborn children, various sexual deviants, welfare mentality, etc…) that the aliens would either seek to cure, contain or eradicate.