Back in the time when drivers Ed was taught and people actually knew how to drive, you were instructed to always accelerate into the open spot when changing lanes and adjust your speed with the flow of traffic after the merge. You were instructed NOT to slow down, and thereby force the traffic you were merging with to slow down.
It is always the job of the merging driver to look ahead and adjust his speed to enable his car entry into the open space. Merging in smoothly and allowing the traffic being merged with to maintain a steady speed is as much yielding as slowing or stopping to let them pass. Anytime you disrupt the flow of traffic in a lane, you are increasing the possibility of an accident.