Why cut the corporate tax rate under full expensing?

Second, that there is some pure “profit,” some pure “rent,” some “unreproducible input” (i.e. something that did not come from a past unmeasured investment), something like the classic “unimproved land” that can be taxed, without distorting any decision. It goes hand in hand with the complaints of greater monopoly.

But I find it hard to find and name a concrete source of profits that, once named, does not distort the decision to undertake some useful activity to make those profits. Starting, organizing, and improving a business, figuring out the intangible organizational capital that makes it a successful competitor, creating a product and a brand name, are all crucial activities for which no investment tax credit will successfully offset a large profits tax. “Intangible capital” is about all most companies have these days.

That is John Cochrane replying to Stephen Williamson, there is much more at the link.  I would add also that Williamson’s model seems to take “r” as constant.