The biggest scam in history is without doubt, religion.
Religion has been thwarting the human race's progress for thousands of years. It is supposed to be a moral and ethical path for humans to follow but is simply violent and divisive and the direct reason for millions of deaths every year.
Religion breeds hatred and promotes inequality, it defines humanity in away it chooses and threatens acts of violence against non believers and those who question its authority.
Religion scams the poor even more than the rich, making unfulfilled promises and lies so the poor accept their hardship to make themselves easier to control. Religion gets richer as the poor struggle to survive. Promises of a heaven don't put food into mouths.
Religion scams people into believing that women are slaves to men, that they are only put on earth to serve men.
I could go on for hours...
Religion - My nomination for the biggest scams of all time