The after-tax cost of debt is lower when the firm's tax rate is higher; therefore, the WACC

Question:

"The after-tax is lower when the firm's tax rate is higher; therefore, the WACC falls when the tax rate rises. Thus, with a lower discount rate, the firm must be worth more if its tax rate is higher." Explain why this argument is wrong.
Cost Of Debt
The cost of debt is the effective interest rate a company pays on its debts. It’s the cost of debt, such as bonds and loans, among others. The cost of debt often refers to before-tax cost of debt, which is the company's cost of debt before taking...