Why is this case any worse than Edward II, Richard II, Isabella of France, or Caroline of Brunswick?
The monarchs you are citing lived in very different times where a Monarchy was seen as the only possible political system (or at least the only one that would be likely to be accepted by a majority of people). So yes, people did accept that there would be bad monarchs and most of them didn't wish for the monarchy to end but hoped the next monarch would be better.
It is the same situation with Gordon Brown: just because a majority of people hates him and his government doesn't mean they wish Democracy to be abolished, they just wants his successor to do a better job.
The situation is different nowadays because people have less and less trouble imagining a Republican system replacing a Monarchy. It's been done elsewhere, and successfully, so why not?
Already, the younger generations is confused as to what role the Windsor still fulfill beside being ribbon cutters and jet-setters.
At some point there was a mystique and a sense of deference for people who embodied British history and a certain vision of Britain, and had a bloodline to show for it.
I don't believe Royals should be barred from marrying commoners, but when they do, these people should bring something really special to make up for their ordinary birth.
By seeking normality, seriously dating a girl with not a single outstanding quality or accomplishment, adding to his own personal failures and image problems, William is failing in the only role that is till being asked of him, imo, which is to embody a vision of Britain people can relate to yet respect and admire.
If he marries Kate and if that trend of marrying dull commoners perdues, the British people will start asking why they are funding or are being represented by a bunch of ordinary people playing dress-up.
As for the people who are arguing that a Royal marriage is a private matter (?!!?) and that the people should just mind their own business, I will just say that this kind of attitude contribute towards the demise of that institution. My opinion.
Those places are as much a part of the heritage of Britain as they are personal houses, and they're also money-makers as tourist draws. I suppose the royals are more like caretakers in that respect than homeowners. It's not like any of them could sell Clarence House to fund a ridiculous tiara habit or anything.
In addition to civil list you have to add the security costs, the costs of organising public duties, etc.
As for the Royal residences, the main reason they are able to enjoy them is because they are the Royal family.
If you want to have an idea of what this family really cost the taxpayer, try to look at it this way: should the monarchy be abolished, what would they be able to still claim theirs?
And that tourist attraction thing is a flawed argument, imo. People do not come to Britain because of the Windsors but because of the Palaces and Castles and all that Royal heritage.
The Queen doesn't do guided tours.
Would the Monarchy be abolished there would be even more tourist money to be made because all the Royal residences could be open all year round, not just when and where it's convenient for them.
Britain would just become like France, whose cultural heritage is still a huge tourist draw three centuries after they chopped Louis and M-A's head.
The history buffs would still visit whether there was an actual reigning family and the star-gazers will say: 'Oh look, that is the chair Queen Elisabeth II used to sit on' and that would be enough royal cachet for them.
