A shared feature of the other contributions to this discussion is that they all think that in the modern world ceremonial monarchies are survivals. That is, they are instances where something once widespread has survived in a small number of places, mainly by adaptation. In a term derived from zoology they are relicts, the scattered remains of a once widespread or dominant political species. The underlying, and unexamined, idea is that they have survived a process of change that has come to affect the entire world and that this change has the qualities of inevitability, unidirectionality, and irreversibility. Quite simply, there is no good reason for thinking this. This is an instance of one of the most pervasive myths or ways of thinking of modern times, the myth of progress. Progress is understood in the myth as being a process of change with the three qualities mentioned and with the additional element that this is change for the better or (often) movement towards a particular end-state, one that is universal, permanent, and the best that can be hoped for. There is actually much evidence against this way of thinking and it should be seen as a mythical or religious mode of thought (I would argue that it is in fact a secularized version of the Christian account of history first articulated by Saint Augustine). In this context the idea is that monarchy is one of the casualties of progress but also for some that we should cherish the relict survivors because they are harmless and bring economic benefits.
There are several reasons why this picture is flawed. The foundational one for me is that it is a specific case of a wider idea about history, which I fundamentally reject. That is that although history may have its eddies and backwaters it has ultimately a unidirectional quality, the course of history moves in one direction and towards a single end. I am as strong a proponent and fan of the way the world has changed in the last two hundred years as anyone, but I think it a serious error to see it as the result of an ultimately inescapable process–not least because of the complacency that this view can lead to. This idea of history is one held by both liberals and socialists of all varieties in both cases. Conservatives also mostly adhere to it but often see the process in darker terms with the present and past viewed through the lens of nostalgia, the dark twin of progress (in the nostalgic vision there is also a process of change that is inevitable, unidirectional, and irreversible, but it is seen as bad or regrettable). I do not have the space here to explain why I object to this view of history (it is my central reason for rejecting Marxism) but in this context it is inaccurate to think that ceremonial monarchy is simply and inevitably a feature of the past because of something called progress.
Apart from reasons to do with the philosophy of history, there are practical reasons, supported by history, for taking a different view. The argument implicit in my co-authors’ essays is that we should keep the surviving ceremonial monarchies but not look to or hope for increasing their number. No country looking to found a new political order and drawing up a constitution should consider moving to or reviving a ceremonial monarchy (for example in the case of an ex-colonial country or one that has escaped foreign occupation or achieved independence through secession). This appears to be taken for granted as obvious.
That though is a comparatively recent way of thinking. Well into the twentieth century, countries in that situation would become monarchies. Sometimes this was done by reviving an indigenous monarchy and dynasty after an interval–Spain being an example of that as recently as 1975. A common practice in Europe was for a newly independent country to import a royal family from elsewhere, usually Germany (at one time royalty was a major German export, along with things such as steel and machine tools). This was done in the territories that gained independence from the Ottoman Empire, such as Bulgaria and Romania, and it survived until the advent of communism. (More recently the ex-Tsar of Bulgaria was the elected Prime Minister there, under the name of Mr. Sakskoburggotski). It was also done in Norway after the independence from Sweden in 1905 following a referendum, and there the monarchy very much survives to this day. There were moves to create monarchies in places such as Finland and the Banat after World War I, and these failed mainly because of opposition from the United States. In the African case of the three High Commission Territories of Bechuanaland, Basutoland, and Swaziland two went down the route of reviving the indigenous monarchy rather than becoming republics (Lesotho and Eswatini). The third, Bechuanaland, became nominally a republic, but for the majority of the time since independence the president has come from one of the indigenous royal families (the Khama family in this case). A similar instance of preserving and making use of an indigenous monarchy (in fact several) is Malaysia.
There is no inherent reason why this should not happen now, and there are sizeable movements for the restoration of monarchy in a number of states in different parts of the world. The practical difficulty of course is a widespread prejudice against monarchy and particularly hereditary monarchy, even in a ceremonial form. This is particularly pronounced among intellectuals and what we may call the political class. However, it would be a mistake to think that this way of thinking is permanent. The history of the last two centuries has shown many sudden switches of opinion, where views once considered retrograde and backward have suddenly become hip and progressive, while ones that were part of the progressive world view (such as eugenics for example) have been abruptly consigned to the darkness. We should not assume that we will not return to the more favorable view of ceremonial monarchy found in the years before 1945.