As I read @Levistus's_Leviathan's OP, the concern is not the label in itself, but the archetype and what it evokes. For me, the concern sits in the same general space as the objection to Orcs et al as "placeholders" or expressions of non-European peoples whose lives and cultures don't really count.
Understanding the connections - what they are, what their nature is, etc - between the Crusades and more modern history is complex, and as I understand it is not something on which there is a uniform opinion among historians. But noting that the paladin, as an archetype - a heavily armed and armoured solider devoted to expressing and pursuing religious ideals - is intimately connected to the Crusades, seems reasonable to me. And I can easily see how coming to that recognition might sour someone on the archetype.
Understanding the connections - what they are, what their nature is, etc - between the Crusades and more modern history is complex, and as I understand it is not something on which there is a uniform opinion among historians. But noting that the paladin, as an archetype - a heavily armed and armoured solider devoted to expressing and pursuing religious ideals - is intimately connected to the Crusades, seems reasonable to me. And I can easily see how coming to that recognition might sour someone on the archetype.