Something liberals particularly tend not to understand is that regulations, especially as we do them, tend to strengthen the competitive position and market power of large, existing players. Conversely, regs also tend to eviscerate smaller companies who are not well-funded.
So when you support greater regulation, essentially you are enshrining the existing players for nearly all time.
This is not always the case, don’t get me wrong. Net Neutrality benefits smaller players more than it benefits large corporations.
However, even regs as salutary as the Clean Air Act mostly benefit those who are already ascendant. It’s always a balance between what will promote true competition and what benefits the public. In this case, regulating Google and Facebook might be worth the cost. Make no mistake, though: by regulating them with any of the proposals I’ve seen circulated will enshrine them nearly forever in their current state.