They have been criticized by governments, parliaments, technicians and each other. Two years ago, for example, the World Bank disagreed with the IMF's handling of the Asian financial crisis. Some of the street protest has echoed the technical criticism, for example, that the global institutions have turned away from their founding mandates and become part of the problem. Both private groups and governments have the right to demand answers to such questions. When citizens don't like the actions of their governments, the democratic solution is to change governments.
Multinational institutions require the same accountability.
That doesn't mean the institutions are less important than in the past or that their policies are always wrong. It's not clear the IMF programs were wrong. The more people inform themselves about these issues, debate them and, yes, peacefully protest if they disagree, the more accountable the institutions will be. If the protests turn rambunctious, the police will do their thing, and Washington's police proved more adept than Seattle's. Many arrests, few injuries.