Maybe not courteous, but at least attentive. If you're driving a manual in stop and go, it's hard to be playing with a cellphone (not that it doesn't happen). You are being forced to spend some thought on the act of driving, which I think is a good thing.

Just go to Italy or Argentina (100% manual) and you'll be disabused of that idea VERY quickly... that's the worst behaving traffic you'll ever see.

I realize you received a few of these comments already, but please also check out India if you think driving a manual improves safety and courtesy.

Manuals would probably shift driving away from the ignorant/nice/slow style of bad driving found in the southern US towards the attentive/aggressive style of bad driving found on the east coast. Definitely not more courteous, but probably more efficient and safer.

Definitely not. Check out any country that is not US for that. Not just Argentina or Brazil, but Europe too. Poland, for example.

(Personally I think everyone would be way more corteous and the roads would be safer if traffic laws were actually enforced. What I mean by that is e.g. ANPRs deployed pretty much everywhere, automatically fining you for speeding. The way most drivers I know treat traffic laws as mere suggestions is ridiculous.)

Check out Brazil.