What you're described is illegal, plain and simple. What the OP described is more debatable.
Laws vary from state to state. Let me make it clear that I'm one that believes that real estate on the roadway should be utilized. Three lanes of traffic utilized up to a merge point creates much less of a backup than a single line of traffic.
The situation described by the OP I believe was very poorly executed by the DOT. The better ones that I have seen that intend for an early merge have traffic cones that narrow the closing lane down indicating that they do want you to get out of that lane at that point, not at an abrupt stopping point.
There is a permanent lane reduction very near where I live on the interstate and it has a sign that indicates that the left lane is closing ahead. The traffic signs from that point read 'lane closure 2000 feet' and continue with declining footage. That lane also contains markings on the road that say 'merge' and that's exactly what happens. Other drivers allow cars from that lane to merge into their lane, light or heavy traffic (stopped or flowing).
The best ones, whether they narrow or not, have a sign that says, 'Alternate Merge.' To go a step further, I believe that any merge is an implied 'alternate merge.'
Quite a few here have gone on and on about inconsiderate drivers and they are assuming that they are correct about when the single lane starts.
I disagree. In fact, I think that those that form a single line way ahead of the merge point are inconsiderate (through ignorance) of other drivers by creating unnecessarily long back ups.
I am an aggressive driver, but a very considerate one. In the situation described here, I always allow others to merge. In other situations, I still usually give the benefit of doubt to the other driver just to be considerate. My exception would be the situation that jtr described above. That's an asshole. Not only would I not let them in, but I've been known to call police.
If I make a mistake while driving, I make it known to the other driver and attempt to apologize through hand gestures. It is usually acknowledged.
And BTW, I've never been intimidated by another driver no matter how mean or ugly they look.