A referendum that is of epochal consequence for a polity needs to be decisive, in order to settle the issue, instead of converting the referendum to a neverendum. Which is why referendums to change constitutions (for those countries that have them) don’t have a 50% threshold; and why federal polities require enhanced majorities of states as well as votes. And given how disruptive the consequences are, the dice do indeed need to be loaded against change, whoever is advocating it.
That’s not Athenian democracy, but neither is anything else in Britain or the West. That is a reasonable check and balance on a popular vote, in favour of stability.
What Cameron was thinking when he came up with this particular referendum is irrelevant to that. The nuttiness of the British political system, whereby you can have a referendum but not deem it binding, is also irrelevant to that.