First, I appreciate your making an actual argument. The OP seems not to understand how to do that.
"People won't invest" is a valid argument, that I happen to disagree with. I believe that people will invest in profitable investments, even if they have to pay taxes on the profit every year. Just like people work for wages even though they have to pay taxes on the wages. It is not a 100% tax. Just as an example using easy number, if they have an asset that appreciates by 10% in year and pay 20% of the gains in taxes, then they profit by 8%. That's still more than the interest I get in my savings account, especially after the pas-as-you go income taxes I pay on that interest. So they won't sit on their money, they will invest.
I believe family farms should be except from all taxes, for many reasons, including food security and that I think much more of the burden of paying for government should be shifted to those who benefit most. But if a developer does buy it for $6M and sits on it while another developer buys your neighbor's farm and develops it, schools and malls open nearby, etc., driving the value of what was your farm to $10M, that first developer just made $4M whether he sells it that year or not. His net worth is $4M more. So yes, let them pay the taxes. I have nothing against him making the money, but I wonder why Uber drivers and mail carriers are being squeezed so that millionaire investors don't have to contribute.