The estate tax is unfair. It is designed to wipe out small business owners so that large corporations can buy their businesses or property at cheap prices.
1.) The so-called "rich" are really small business owners or long time, multi-generational property owners who have seen the overall value of their business or property go way up over the decades. They die and the heirs cannot pay the estate tax so the business or property must be sold immediately to pay the estate tax. Corporations know that they can then snap up the property at fire-sale prices.
2.) The so-called "rich" have already paid income tax throughout their lifetimes. The estate tax is just another, extra tax levied on those who happened to have worked hard and been, yes, a little lucky. These folks want to pass the home or the business to their children but cannot because the estate tax must be paid. Hence, the home gets sold or the business must be given up.
3.) I reject the whole crazy argument that "only a few people pay the estate tax" so therefore there is nothing wrong with it. That's like saying, hypothetically, there's a new rule that says someone will be randomly executed by the government but don't worry because very, very few people will actually be randomly executed. "What's the harm? Very few are affected." It's not very fair to the person who is randomly chosen to be executed, however. So, just because a few people are treated unjustly doesn't justify the tax.
4.) the estate tax is a windfall to the insurance companies because to have the money on hand when you die to pay the tax you must buy expensive life insurance premiums so that your heirs will have the life insurance proceeds to pay the tax when you die. Insurance companies love the estate tax because they get these high premiums.