And why shouldn't it be?
We can ask the "why should A be taxed?" question on anything we don't want to see taxed. It doesn't make it decisive.

There must be taxation (or rental of the commons) as long as we want to have a government (and the alternative is Somalia, not Ayn Rand fantasy). There is no a priori reason to tax A rather than B. Ideally, we'd like to tax negative things more than positive things -and so wealth more than income since it has more negative consequences. But, of course, externalities even more so.

Besides, any tax on the value of houses would be priced in so only a sudden major hike after buying would have a significant negative effect.

Also besides, there is nothing inherently virtuous in saving

Also also besides, refusing taxes on wealth is the ultimate fait accompli policy. All you need is a few years of conservative governments, those in position of power make out like bandits (think Russian oligarchs) and thereafter maintain a huge position while the plebs who need to work for a living suffer through years, nay decades of adjustment. Rinse, wash, repeat.

Earth provides enough to satisfy every man's need, but not every man's greed. Gandhi

We can always tax your wealth away through inflation.

tens of millions of people stand to see their lives ruined because the bureaucrats at the ECB don't understand introductory economics -- Dean Baker

Nobody ever got wealthy by declaring their income, not dodging any tax, and declaring all their wealth. Well, maybe Warren Buffett...

Now seriously, why is this funny?

tens of millions of people stand to see their lives ruined because the bureaucrats at the ECB don't understand introductory economics -- Dean Baker

Why should the value of that home be taxed again?

It should be taxed because ownership of that home is supported and protected by most of the expensive services provided by government from fire and police to the title registration in the county registrar of taxes. Sure, it is the representation of accumulated wealth, but it is the holder of that wealth who benefits disproportionately from the services of the society that protect that wealth. "The law, in its majestic equality, forbids the rich and the poor alike to sleep under bridges,...". It lowers property values.  

"It is not necessary to have hope in order to persevere."