I definitely appreciate you taking the rime to respond. I’m just not sure that I agree that a network effect is monopolistic. It feels more akin to losing a feature by switching off gmail.
Definitely valid points about turning off the filter, although on gmail, I believe that is only for your personal filters. Google still filters huge amounts of malicious stuff before it gets to the spam folder, by silently dropping it.
A natural monopoly is a monopoly in an industry in which high infrastructural costs and other barriers to entry relative to the size of the market give the largest supplier in an industry, often the first supplier in a market, an overwhelming advantage over potential competitors.
Source there: https://en.wikipedia.org/wiki/Natural_monopoly
A social network is very similar to railroad network, electricity distribution network, or landline phone network. Yet we allow Facebook or Youtube to do whatever they please with the servers they own, while regulating the hell out of the older ones.
People [would be] consuming the spam content being filtered agree with the filtering and are generally happy with it.
Failing that, when people are unhappy with their spam filter they can adjust or disable it.
As a last resort, they can migrate to another e-mail provider, there's no monopoly on e-mail. Moreover, e-mail is delivered almost equally between different providers.
Many people watching youtube or reading facebook are unhappy with their content policies. There's no way to control their filters or opt out of them. There's de-facto monopoly on these markets: the network effect is too strong, and antimonopoly laws don't seem to apply to their acquisitions of competitors.