If Washington and London allow the gruesome events that are unfolding in Egypt without acting decisively, then any claims that they are champions for freedom and democracy will never be believed again.
Since the events of 9/11, America and her allies have always said their actions were dictated by the desire to bring democracy to the Middle East and further.
That was the rationale behind the invasions of Afghanistan and Iraq.
It was also the reasoning behind supporting rebels in Libya and more recently Syria.
And now those very countries are offering little more than lip service when a military conducts a coup against a democratically elected President, and a bloody crackdown aimed at breaking the largest single political group in Egypt.
Friday has been designated as a ‘March of Anger’ by the Muslim Brotherhood, a response to the appalling putsch on Wednesday in which at least 638 people were killed.
If the Brotherhood are to believed that figure could be more than 2,000.
Already, the Egyptian authorities have been preparing the world for more bloodshed by choosing which pictures are broadcast live.
Alongside images of walking protesters, shots of armed men firing into where it is not clear, are being shown. This is, according to BBC correspondents a defining day, a fight for which narrative gets heard and accepted. It is also an attempt to restore order and get Egypt back onto a stable economic footing following the turmoil brought about by political crisis. It is none of this. Today is a protest against a military coup that has killed hundreds, and promises more bloodshed.
And if the powers that can influence the Egyptian military do not act, then they will send the Arab world’s most populous country into a downward spiral of never-ending chaos and anarchy. And in the process, they will reveal the bankruptcy of their own foreign policy.
That will mean the end of any future talk of humanitarian interventions.