The ISPs have put up astroturf advocacy groups. You might actually be listening to the ISPs themselves, thinking they are just freedom-oriented groups agreeing with the ISPs. Many groups that aren't actual astroturf have also been paid off by the ISPs.
you think the government should be able to force every domestic shipping company to charge the same flat rate for every package - regardless of weight or size - that the post office charges for a letter
What you just described is not net neutrality. The ISP astroturf organizations and the Democrats have been successful in confusing the issue to their own ends.
But that is what is in the Markey Net Neutrality Bill. That is what the FCC is calling Net Neutrality.