One can find advocates for just about anything online, and monarchy is no exception, with no shortage of both pro and anti sites. I will now look at some monarchist arguments and try to analyze them. Arguments for Monarchy – Monarchist Manifesto has a sizable number of them, ranging from the fatuous “In a Monarchy the monarch represents all the people not a certain majority or minority but all the people” to the more serious “Monarchs are by the far the most effective barriers against dictatorships. Had there been a Kaiser in Germany in 1932 I doubt Hitler would’ve risen to power. Had Tsar Nicholas II been in charge instead of Kerensky it is very likely that Lenin could’ve been stopped.” Paralleling the latter argument, Constitutional Monarchy vs Republicanism…? – Yahoo! UK & Ireland Answers features the argument that constitutional monarchies are more stable than pure republics, giving as an example that Adolf Hitler came to power in a pure republic.
There is plenty of counterevidence to the anti-dictatorship argument. King Victor Emmanuel III of Italy did hardly anything to stop Benito Mussolini, and Emperor Hirohito of Japan was even worse, supporting Japan’s war efforts. So if Germany still had a Kaiser when Adolf Hitler became Chancellor, the Kaiser would either have gone along with Nazism or else Hitler would have forced him to abdicate — or suffer an even worse fate.
The stability argument reverses cause and effect. Monarchies are often abolished as a result of big political upheavals, and nations that do not have such upheavals tend to keep their monarchs. Thirteen British North American colonies’ War of Independence was the end of the British monarch’s sovereignty over that territory. But the other big “Anglo” territories, Canada, Australia, and New Zealand, never went through anything similar, and they are still subjects of the British monarch.
Outside the British Empire, France’s monarchy was deposed in the French Revolution, though it made a brief comeback a few decades later. World War I resulted in the end of the German, Austrian, Russian, and Ottoman monarchies, but not the British one, because Britain was less affected by that war than Germany, Austria, Russia, or the Ottoman Empire.
I’ve seen various other arguments, like the touristic value of the British monarchy. However, national-heritage tourist traps do not need monarchs.
So I (lpetrich) do not see a good case for monarchy.