Plenty of discussion on this in the past. Do a search.
But basically by reclassifying the ISPs as common carriers meant that they had to treat everyone the same and not prioritize services by fee or content. Sounds great to liberals, but breaks down in practice, because Netflix demands are much greater than Mario's corner pizza shop. So ISPs must upgrade their networks to transmit Netflix traffic, but can't charge Netflix more money for the transit. So if the ISPs can't charge Netflix for the usage, guess who gets to pay the bill at the end of the day?