A constitutional monarchy is an unreasonable construct, but its perseverance is a symbol of continuity and certainty in an existence that is so often chaotic and uncertain. It provides reassurance to many, and mutes the worst excesses of political turmoil. As long as it really stays out of the fray (and that's sadly not always been the case, with Elizabeth II, and it's likely her son will be even worse), then I don't have a problem with it. Like religion, I don't need it, you don't need it, but many do - and they might as well have it.