I'm all for reigning (

) in the scale of the monarchy, getting rid of all the lesser royals and the assorted hangers-on and I'm not a supporter of hereditary power in itself, however I think it's still the best option to keep the King/Queen as head of state.
The biggest single reason is just how uber-s*** the alternative is. Ask yourself what group you hate even more than the royals and I bet my arse that for most people, even the republicans, politicians is the word that springs to mind. So why would you want even more of them with even more power to f*** our lives up, for f***'s sake!?! Our politics is already f***ing pathetic and having a president would only accelerate that exponentially, putting us over-the-top and well and truly into La-la land like you see in the states. I can't imagine anything worse myself, it'd be f***ing awful, I think I'd have to leave to be honest.

A constitutional monarchy with a ceremonial head of state, is the least worst option by some way.