That's fine if you can safely merge into the exit lane without slowing down traffic in the non-exit lane.
Here's when it's not OK: cars in the exit lane are traveling at 2mph. You drive up next to the line, slow down from 55mph to 2mph and wait with your blinker on for someone to let you in. Now you've slowed a second 55mph lane down to 2mph, blocking thru traffic and creating a dangerous stoppage in the non-exit lane.
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.
Perhaps a more advanced camera technology that detects asshole driving behavior instead of speeding? Rich dudes pay to get ahead. Increased revenue for the police department. Improved traffic. Win-win for everyone.
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
Here's when it's not OK: cars in the exit lane are traveling at 2mph. You drive up next to the line, slow down from 55mph to 2mph and wait with your blinker on for someone to let you in. Now you've slowed a second 55mph lane down to 2mph, blocking thru traffic and creating a dangerous stoppage in the non-exit lane.
Seriously, don't do this.