Why do people become unhinged when you drive exactly the speed limit?

[Anonymous]

I have been doing a lot of highway driving recently and have seen drivers do unbelievable things. In the past few weeks I saw a car from far left lane move over 3-4 lanes to take exit only to start to get off at ramp and then drop back into traffic and cut all the way back over to original left lane. It was like watching something in a movie. There are motorcyclist that weave in and out of traffic or drive in between lanes at high rate of speed. A Volvo wagon was speeding and weaving through traffic last weekend on 395 - it looked like they were trying to evade police. These are just things I have seen but am sure there are many more. How is this acceptable??