Assets like housing or businesses coming to market more frequently is a good thing because it makes them more affordable... rents go down etc. That's the main benefit of the inheritance tax - redistributing wealth from those who haven't earned it (e.g. by inheriting) to those who have (by working), and democratising ownership of the productive parts of the economy.

The cyclical nature of the economy undermines as well as supporting your argument. You will admit that it's possible that a family being forced to sell a firm at the height of a boom might even be grateful for the inheritance tax, as if they had not been forced to sell, the resulting crash might have wiped out its value.