[roc]

To be fair, I think their argument is more accurately phrased: the government is more deserving than the heirs (after a reasonable threshold, natch). Or, more generally, society is more deserving.

I don't see a logical conflict in their preference for private charity over government redistribution.

Honestly, I don't think any proponent of the estate tax would mind if the practical result of a high estate tax was that the rich just gifted their estates to private charity to spite the government. Government is just the only group with a sufficient cudgel to enforce the practice and sufficient reach to ensure that otherwise-undirected estates do give back to society.