They never got a chance to express their ideas on the Monarchy. Neither in 1919 nor in 1945/55 could they vote on the question if they wanted Crown Prince Otto as their Monarch or not.

Not exactly. He seems to have been advocating democracy as a means to a monarchy!

That’s rubbish – because the legitimate system in England rests on being called to the throne by the successor institution of the Witanagemot, the Council of Accession, and that never called that Prince to the throne.

“The clinging to legitimism of the Duke of Chambord thwarted the restoration of the Bourbon kings”.

Actually, no, it didn’t. It thwarted the restoration of the Duke of Chambord as a “king of the French”, resting on the idea of the people – an approach that had already been tried between 1830 and 1848 and had left the way open to republicans. The Duke of Chambord accurately realised that only the legitimist approach could prevent the throne again being undercut by republicans, and gambled that opinion would move to allowing the legitimist approach. It didn’t, it built support for the provisional arrangements (the Third Republic). A better approach would have been to accept without making any oaths or commitments, and allow a later king or kings to build support for the institution (as happened over generations for the Hanoverians in Britain).

What is completely missing from von Mises’s position is an understanding that “the people” is not well defined, and of the implications of that. That is, any definition of “the people”, in a system based on democracy, is a circular argument. On the other hand, this question does not arise under legitimism; “The democratic monarch may not deal even with Republican-minded citizens as enemies; doing so would compromise the dignity of his position” misses the point that there are no such things as “Republican-minded citizens”, for there are no citizens and anyone who is “Republican-minded” is an outsider anyway – defined out. This creates the separate problem of whether legitism can be viable without full support, but it is a problem of tactics rather than the fundamental inconsistency and self-contradiction of a citizen-king yoked to adversaries; the enemies do not go away, but they are without rather than within where they cannot be escaped – which is what befell Louis-Philippe as “king of the French”, and which the Duke of Chambord sought to avoid.

In the circumstances of the time and place in which he was writing, it may well have been that von Mises was writing tactically, to work towards what was realistically attainable then and there. Nevertheless, if so, he was certainly not writing for the ages – and in particular, not for this age.