Debt financing has a tax advantage over equity financing, as the borrower gets reimbursed the tax on interest payments and other debt-servicing costs. Thus $$ R_{\text{WACC}}=\frac{E}{E+D}R_E+(1-T_C)\frac{D}{E+D}R_D $$ where $R_{\text{WACC}}$ is the weighted average cost of capital for the borrower (a firm), $E$ is the market value of equity, $D$ is the market value of debt, $R_E$ is the cost of equity, $R_D$ is the cost of debt and $T_C$ is the corporate tax rate.
On the other hand, the lender does not get $R_D$ but only $(1-T_C)R_D$ after tax. So if the lender actually wants to get $R_D$ after tax, they need to charge $\frac{R_D}{1-T_C}$. Question 1: Is that a useful way of thinking about how the lender actually sets the required rate of return?
Question 2: Consequently, if the corporate tax were abolished, would we have $$ R_{\text{WACC, no tax}}=\frac{E}{E+D}\tilde R_E+\frac{D}{E+D}\tilde R_D $$ with $\tilde R_E=R_E$ and $\tilde R_D=\frac{R_D}{1-T_C}$?
(I guess not, as the equity holders also pay corporate tax. If they were to follow the same logic as the lenders, then they would also set their required return to $\frac{R_E}{1-T_C}$. This way the effect of tax would not change the ratio between $R_E$ to $R_D$.)