Not only does a manual transmission help, but it kind of pushes everyone into that kind of driving. Maybe it's just because you don't need brakes as much. When I drive an auto (usually rental), I find I'm a lot more aggressive.
I also fond that places with a higher percentage of auto drivers are heavier on the heavy traffic scooch-and-brake.
It's not a straight conversion to aggression. Germans, I believe, drive fast. Maybe aggressively too. But, if you put them in an auto, they also pick up the behaviour of building speed fast for 1-2 seconds then braking hard. It happens a lot in dense, halting traffic. It's not the only way of being aggressive, but it's another way
People don't do that in a manual because it's not fun.
*In Italy people drive mostly manuals. They also drive like suicidal grandmas in fast forward.
I also fond that places with a higher percentage of auto drivers are heavier on the heavy traffic scooch-and-brake.