towardsutopia21

I think I didn’t state my question clearly.
When add back interest to Net Income to get to FCFF, we tax affect it, because theoretically, if you didn’t pay the interest expense, then you wouldn’t have the benefit of the tax deductibility of that interest expense.
Why does the same logic not apply to D&A? i.e. if you didn’t pay the D&A, then you wouldn’t have the benefit of the tax deductibility of that D&A? Is the answer that we are adding back the D&A due to its being a noncash expense, whereas we are adding back interest expense for a different reason, i.e. to determine what cash flows are available to the firm?