The justifying argument is generally that all other forms of government are even more corrupt that democracy. This is questionable in practice as democracy seems to be a peculiarity of western civlization, and doesn’t seem to work very well elsewhere. In india for example, corruption is so pervasive that the country stagnates. Whereas in China where the government is very strong, and now an oligarchy, the government managed to make everyone literate and move the economy much faster than India.
Consumer capitalism and property rights are meaningful exports. THe tradition of democracy looks as though it has proven to be a failure outside of western Europe – where corruption is simply very naturally low due to ancient cultural reasons.