Taxes are cash outflows......and are no different than other factors of production.
Income taxes are different. They are not required to producing anything. They are
not a factor of production.
Profit planning is sophisticated, and immediate, mid and long range. Any absorption rate that does NOT include taxes is just WRONG.
I assume the point of a profit plan is to figure out how to make as much profit as possible? How would paying an income tax affect this goal? And how would it affect the price a company gets for it's products or services?