> Suppose the car in lane 1 is going slower because they just merged from a left-side entrance ramp.

Just to clarify, my original post was more about merging from a faster lane of travel into a slower lane, or where both lanes are traveling at about the same speed.

When merging into a faster lane I agree the slower moving car should wait for a suitable opening before signaling and merging. And there are cases where it is safer to pass a car with its blinker on than to slam on the brakes.

But also in general it's unsafe to be traveling at a large speed differential to the lane next to you. And a lot of times even though people probably could ease up a bit to make space for another car, and it would be safer to do so, they don't.