For me, it's not empathy. It's gas mileage. I burn a whole lot less gas when I'm coasting in 2nd gear than when I have to come to a dead stop, accelerate, step on the brakes again, etc.

I've found that usually people who will cut in front of a gap accelerate pretty quick - after all, they're hopping lanes so they can do that. I rarely need to slow down for them, although occasionally some asshole will misjudge distance & speed.