I know exactly what and where you are referencing here. When traffic is stopped on the highway, doing a "zipper" merge is really the best way to keep the traffic moving- both the traffic already on the highway and the traffic trying to enter the highway from the ramp. Yes, the merging traffic from the ramp is required to yield- but in a practical sense, the traffic from the ramp would never move if every car on that ramp just yielded stopped and waited. All it takes is one or two aggressive drivers to gum up the works. It's all about being predictable... and aggressive drivers are not.