The United Kingdom's Adam Smith Institute notices that "republican" — i.e., anti-monarchist — protest has essentially been banned from the upcoming royal wedding, and calls that a shame.
The item goes on to argue that while in theory there isn't much theoretical support for the idea of constitutional monarchy, in practice, "the record of modern constitutional monarchies has been a good one for tolerance, for the rights of dissenting minorities to do their own thing, and for upholding the rule of law and the rights of free speech."
The Adam Smith Institute doesn't give a list of the "modern constitutional monarchies" it is using as a sample, but it's got to be a pretty short list, and it may be that the countries on it share some other qualities in common.
As the author of a biography of Samuel Adams, I'm no fan of the British monarchy, "constitutional" or not. If the alternative were the Soviet Union, Communist China, or Nazi Germany, all of which lacked kings or queens, I'd choose to live under the British monarchy without a moment's hesitation. Fortunately, there are other alternatives.