instead of getting rid of it at death. The kids would take the built-in gain, but if they never sold the stocks, they’d never pay the tax either.

The step-up really just enables the kids to sell the stocks without realizing (and paying a tax on) the gain that their parents, not they, experienced. Which is one rationale for the basis step-up.

That said, agreed that getting rid of the basis step-up is unlikely; it’d represent a much more wholesale change to the American tax system.