I don't understand. Net neutrality was the default state of the early internet. The internet wouldn't exist as we know it without this guiding principle. It is only the recent deviations of this principle by providers that has prompted the movement to codify these ideas into laws.
There were no "net neutrality" regulations in the US till 2015. Nevertheless none of the horror scenarios net neutrslity proponents like to cook up came to pass, and in fact the 'Net grew to "the Internet as we know it" precisely in an era of no net neutrality regulations. That's ample proof (if any were needed) that all the net neutrality FUD is just that.
In a free market, if an ISP was to mess with the traffic going through its pipes, that would just encourage anyone who cared about this to switch to a competitor.
The real problem is the lack of a free market, which is the direct result of over-proliferation of laws and regulations, which discourage and stifle innovative businesses. Net neutrality regulations are just another layer of these, and will further cripple innovative competition and lead to increased monopolization of Internet infrastructure by big crony-statist corporations.
More fundamentally, it is a violation of basic individual rights and property rights for the government to tell any private enterprise how to operate its business. That's the economics of fascism.