I see this all the time in Massachusetts - Route 2 West to Route 95 North, about a mile from my home. At rush hour there are always enough jerks playing the "merge at the last minute" game that only the left lane is still moving significantly, and sometimes not even then. Every once in a while there's an accident because people who were unaware of this "congest all the lanes" behavior didn't see a blocked left lane soon enough.

You're right, it's a major dick move. It's reckless and endangering; police should treat it accordingly.

Have you blocked through traffic? Only if the number of cars per second drops. Also as there's going to be a queue of, say 1000 cars behind the merge point, it's better than the queue doesn't extend backwards into some other area of traffic, causing people who are turning off before the merge point to become involved in the slow traffic

You don't have to let me in. I am sure someone in front of you will. Then you have the right to throw a little hissy-fit because of having to live with the repercussions of your poor life decisions.