Both the opponents and proponents of net neutrality agree that the goal is an Internet which is flexible, inclusive, affordable and democratic as possible. They differ in the method how to achieve this goal.
The opponents of net neutrality argue that the best way to achieve the above is by an unfettered free market. They argue the opportunity for profit and competition will result in the best outcome for all.
Proponents of net neutrality believe we need to have an additional safeguard in the form of government regulation. This is driven, in part, by concerns about how free markets tend to consolidate resulting in monopolies and oligopolies. Without this safeguard, they argue, the Internet will follow the same path to consolidation as banking, finance, oil and energy and traditional media.