One way to look at the current crisis is that a whole lot of long term plans, once thought to be sensible, were abruptly shown to be unworkable.
These plans included actual inventories, lines of production, houses and other buildings, and actual people working at actual jobs to support all of these.
Those plans now have to be scrapped. That means inventories wasted, lines of production shut down, and people fired. We cannot just keep building more and more houses as if nothing has changed.
Shutting down production lines and firing people is a real destruction of wealth.
This destruction will have secondary and tertiary effects. We've already seen how the cascade works in the stock market. Over the next year (or more) you will see it in production and employment levels.
> The crash of the financial markets has not reduced the production capacity of any of these goods or services.
It has, because a considerable fraction of that productive capacity was allocated based on false assumptions.
We have to reallocate that productive capacity to new purposes. We don't yet know exactly what capital and labor needs repurposed, or to what new purposes. The way we find that out is by businesses contracting or going bankrupt and people being thrown out of work. Eventually, other businesses will expand, new ones will start up, and people will find new jobs. It will take a while, and in the meantime, it is going to hurt.