“Why are they confident?”
4 reliable statist liberals, 2 of whom Obama appointed
1 squish who most likely would not go out on this limb
1 true constitutionalist (Thomas)
3 conservatives who should be solid
5-4 upheld would be the over-under on this. BUT Kagan should recuse AND Kennedy should over-turn ... to get you to 5-3 overturned.
I hope!
Otherwise, ObamaCare stands. This SCOTUS is NOT going to overturn the New Deal Commerce Clause.