[pyth0]

You don't have to be religious to recognize that this is the stated reason for which the royal family was given its legitimacy. Obviously that is not the sole reason for its continued existence, but (as an outside observer) all of the rituals and ceremony surrounding the coronation seem to further entrench that idea.

[AnimalMuppet]

But religion was also the stated reason given for the legitimacy of the US revolution. "We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain inalienable rights..."

The US becoming far more atheist doesn't undermine the legitimacy of the US democracy, even if the original stated basis isn't regarded as valid any longer. The same can be true of the monarchy.

Mind you, I'm not actually a supporter of the monarchy. Where I'm from, we don't bow to monarchs. I'm just saying that this argument against the monarchy does not seem valid to me.

[George83728]

The US Revolution kicked the British government out of the region that would become the United States, but did not itself create the government that the US operates under. That happened 13 years later, when the present secular US Constitution went into effect.

[mixtur2021]

Nuance there is that the legitimacy in the form of line of succession has been governed by law too (and no doubt conquest historically) at least following the glorious revolution of 1688. It has jumped around.