hamish beat me to it here.
His torture of Gollum happened long before the Fellowship was formed, so this too points to a colossal stupidity on Sauron's part specifically. He should have taken one look at that thing, said "jesus, you had my ring how long? And you' didn't bring it to me or get yourself killed in all that time? You're clearly a dangerous people!"
Again, it's just abject failure to know his enemy.
Shoving him, no - but going over the edge with him to save the world, tears in his eyes, sacrificing both of them - I could totally see Sam doing that.
Sure, but the guy carrying/wearing it gets the brunt. Otherwise Sam and Elrond would also be "Man, you're so right, we should totally keep this thing and not go anywhere near the fire." And Boromir did fight it off, while the others (who had been around it just as long as he had) didn't even notice. If it can't corrupt bystanders equally to the guy carrying it, and doesn't help the guy carrying it fight off said bystanders, that's a critical design flaw.