IMHO, the morality of the estate tax lies in its ability to ensure that no level of wealth is accumulated that effectively turns descendants into dynastic wealthy. My opinion is that the estate tax should continue to exist, but should apply only to levels of wealth that would otherwise allow the dying person to put his/her direct descendants in a position of not ever having to work.
Below that level is where the problems come into play. While various forms of estate tax have existed since ancient Egypt, typically the tax has only applied to wealth beyond $5-10M in today's dollars = roughly the threshold I mention above. With the fiscal cliff (short-term) and chronic deficit spending (mid/long-term), we who care need to make sure the majority doesn't infringe on the fiscal minority's right to fully pass on assets that, far from creating dynastic wealth, merely ensure that children and/or grandchildren have small nest-eggs to start their adult lives with.