How do governments justify the imposition of death duty or inheritance tax?

There is no justification for it, it is simply and plainly a money grab by governent after a person has died. There are many exemptions and clauses to it, many situations where only when the amount inherited is over "insert seriously large amount of money" amount do they take 1% or 3%. Some US states (Utah, New Hampshire) abolished inheritance law (Estate tax) recently, some countries have never had it (Cayman Islands) and some coutries have "always" had it and now treat it as one of those peculiar and sucky laws that you just have to live with (the UK).

Essentially though there is zero justification for it, logically, morally or legally except in the eyes of government.