[johnnyanmac]

>If an inheritance tax has to be applied, this means society has already failed to stop runaway wealth accumulation and inequality.

Yes. And we are already on "too late" mode. So we should go with the 2nd best solution because the best one (actually taxing billionaires) won't work retroactively.

>I'd much rather we have checks in place to stop individuals from accumulating megawealth in the first place (or at least slow it down), rather than relying on an inheritance tax which takes effect long after the accumulation happened.

Both would be nice. I don't see this as mutually exclusive. Though proper wealth taxes will lessen the need for inheritance tax. But not in all cases.