The question in more detail is, generally speaking, any time you are driving and you will soon occupy the same space with another vehicle (crash) unless one of you speed up or slows down to let the other guy get in line, which do you do? Are you the one who speeds up to get in front, or do you slow down and let them go in front?
I don't understand the question.
If I am driving down the freeway in the right lane and I pass an on-ramp with cars travelling down, I shift into the left lane so the car can get over.
If I am driving down the freeway in the right lane and I pass an on-ramp with cars travelling down and I can't get into the left lane, I continue at my current speed since the onus is on the merger to make a safe transition.
If conditions are poor, I am always more cautious and will drive slower.
I would never ever speed up to "let" someone in behind me.
In congestion while travelling slowly, if I am in the right lane and passing an on-ramp with cars travelling down, I leave space between myself and the car in front.
Regardless of anything, if all else fails, it is 100% the onus of the person who is merging onto a freeway, into traffic, or onto an exit to do it safely. This rule has no exception and is without fail.