People with street-legal cars should still have the right to drive them on private roads if they want to. This law restricts that.
Are you saying it’s more important for people to have the ability to drive road-legal cars dangerously on private property, than it is to prevent fatal accidents caused by drunk drivers?
Would you complain that you couldn't reach speed greater than 20mph on stock electric scooter?
Surprisingly, but absolutely, not true. For instance, in most places in the US at least, you can be prosecuted for DWI on a private road on your own property (as it is about operation of a motor vehicle regardless of place).