If I'm driving a car I always make sure to not leave enough space to merge for drivers who do that. The unnecessary merging it causes disrupts optimum traffic flow and well, I guess in my own head they won't stop unless people quit being nice and they are forced to drive off the road, or stop and do the merge of shame with a long line of traffic going by.
To play devil's advocate, who says that maybe some of those people are in an emergency situation where they need to get to their destination very quickly? A while ago, I was quite ticked off at a guy who was zooming from lane to lane in what I thought was unnecessary merging. Then he turned into the ER at the hospital.
That's an extreme example, but you just never know what's going on in the heads of other drivers. I let people in now, but I still have a problem if they don't signal. Use your signal and I'll let you in with no problem. I always leave a space in front of me, because people tend to ride their brakes and I never realize how hard they're actually braking until I see them at a standstill.