Here's the Network Neutrality elevator pitch:
In a competitive market, I would buy the telco and cableco arguments. Their sector is very strongly regulated. There is little competition outside of their comfy duopoly. Thus, if they're given the chance to sell high speed to some people, and low speed to others, what will really happen is that no extra bandwidth will be offered. Instead everyone will get the low speed unless they pay. This is the equivalent of "Nice website ya got there. You wouldn't want anything bad to happen to it, would ya?"