Why does the UA pick and choose what it accelerates?
It does not. It accellerates eveything equally in the known universe.
Umm... then why aren't we weightless?
If you are on a ship and on the leeward side of a sail, you would not feel the wind pushing on you but would still be traveling at the same speed as the ship.
You explicitly claimed "It accellerates eveything equally in the known universe",
Then you claim that things on the earth are shielded, but surely "eveything equally in the known universe" includes the "things on the earth".
And if these things "on the earth" are shielded, how high does this shielding go.
Polaris is not that far above the earth (3,000, 4,000 who knows) and is around 12,400 miles from the "edge" (but where is the edge?), so how is it shielded by the earth.
Seems all a bit hit and miss as to what gets "shielded" especially as no-one has any idea what sort of a force could push on the earth and push on the objects above the earth, providing exactly the same acceleration (not force) to each.