In the "family farm" (and "family business") scenario, we're talking about private companies -- whether incorporated or not, all the owners are related. If part of such a company needs to be sold off to pay taxes, it would presumably be sold to a someone at arm's length, which would fundamentally change the business structure -- just like running a startup with VC investors is different from running a bootstrapped startup.
There's not many plausible routes to "paying the millions-dollar death tax so that developers don't turn the cornfield into a suburb" in such scenarios. Mostly moot though, this all played out and was over before most of us were born. I suppose there are gigantic 20,000 operations that "won't stay in the family"... but those farmers:
1. Aren't really living on the same piece of land that they farm
2. Having to sell off 1500 acres to pay the tax bill doesn't much affect their operation except that it's slightly smaller
3. Have someone custom combine it anyway... they're basically a management company that hires a bunch of contractors
4. Generally are incorporated in such a way that sole ownership hasn't been an issue since great-great-granpa died back in 1961
Family farms are, at this point, largely mythological.
1. Continue operations of the family farm, assuming you can come up with the money to cover taxes.
2. Sell the farm to Big Farm, Inc., get a $5M check and forget about it, regardless of the consequences that means to your customers.
Inheritance, even with normal tax, is a cheap way of keeping money in the family and keeping rich people rich. It is not based on merit, capabilities or need and serves no purpose in a society based on improving the lives of the entire population. (Which you can argue is not what [country with low inheritance tax] is)
I would say that society is served well by the ability of widows to inherit and not be left destitute. Similarly for minor children.
If you're talking specifically about inheritance by adult children, I agree the arguments in favour are weaker.
If you have $300 to your name, you're not getting finance. The bank will just laugh you out the door.