Since I lost karma for that, I'd better elaborate. Your specific quoted line shows that protection was the reason for the ghetto's placement, given that they were going to have one. It does not say that protection was the reason for having a ghetto.
Your own link says that "Jewish ghettoes in Europe existed because Jews were viewed as alien due to their non-Christian beliefs in a Christian environment". The only mentionthat is anything like what you claim is halfway down the page, has no reference, does not name the location of the ghetto, and neither 1) says whether Jews could live only there or 2) if so, gives a reason for why they were prevented from living anywhere else.
That link says that ghettoes were used to protect Jews in the manner you describe. It does not say that that is why ghettoes were created.
It seems to me that we should separate the claim that the actual historical motivation of creating ghettoes was to cause harm to Jews, and the claim that there was no reason to make them besides causing harm to Jews. If there is one reason that Jews benefit from living separately from Christians or Muslims, then we can't make the second argument.
But I don't think we can make the first argument, because we can't genera...
Another month, another rationality quotes thread. The rules are: