You put forward a very convincing argument, Sir.
From my fading memory of visiting Paris, aren't some of their buildings linked to their royal families pre revolution?
The only main royal historical site that i can think of that you can't access in entirety is Buckingham Palace, for obvious...
If you're 'anti-royal' that's fine.
Of course it's difficult to quantify how much money comes into the country as a direct result of the Royal Family, but I would imagine that it's a big reason for tourism. Yes, there is other heritage, but I would imagine it's doesn't have quite the pull...