But......at the moment when you want to repay that debt, you need to sell the shares = pay tax on them. You can of course pay off the debt in some other way, but presumably whatever money you use for that purpose would have been taxed too, perhaps even more so than shares are.

And I mean, if I borrow money to help me out until I get my paycheck, I don't pay the income tax on the borrowed money - I pay it when I get the paycheck.