As a user I found Facebook's contact importer to be useful, and LinkedIn's to be deceptive. Zynga was a terrible spammer /on/ Facebook, but Facebook eventually cleaned that up (too slowly, but they did).
Google's growth was organic and based on a very high quality search product. The spammier search engines all basically died off.
So I disagree with your premise that Silicon Valley success is generally based on spammy or unethical behaviors. Yes there is way too much of it, but no, it's not a necessary part of success.
Google is an extremely rare example of natural growth. Many found Facebook's contact importer in its early days to be deceptive (and many more still do). Their growth to more than a billion users was almost inevitable - as long as they could spam dozens or hundreds of people for each new user. LinkedIn is yet another example of success-by-spamming, and Facebook's "cleaning up" of Zynga and thousands of other smaller, similar businesses built on Facebook is an example of what I was referring to when I said that companies block the very kind of behavior that got them to where they are once they are big enough to do so. They do whatever they have to do to get through the door, then they shut it behind them.
Is spamming/other bad behavior "necessary" for Internet success? That's an interesting question. I can only think of a small handful of successful Internet companies that magically went viral without such aggressive "growth hacking". The overwhelming evidence is that "necessary" may be a strong word, but "highly unlikely without it" is probably an accurate description.
Define "early days". The early days I remember everyone was waiting in anticipation for the moment their university (and later on, "Network"/company) would be on Facebook. There definitely wasn't a contact importer in those days, because the entire platform was exclusive.
Google took the opposite approach, which was to play the iconoclast that was not evil and once they won the market, to start being shady and use dark patterns everywhere.
Google's growth was organic and based on a very high quality search product. The spammier search engines all basically died off.
So I disagree with your premise that Silicon Valley success is generally based on spammy or unethical behaviors. Yes there is way too much of it, but no, it's not a necessary part of success.