Normally I think your posts are very thoughful, but this time you are attacking a straw man. The OP clearly indicates near the bottom of the post that it's not about working for the betterment of humanity, but about work he personally finds fulfilling. Serving ads is not fulfilling work for him. Morals don't come into it.
The OP was attacking a strawman. The assertion that Google and Twitter and Facebook are not working for the betterment of humanity (or are not doing fulfilling work) because they sell ads is ridiculous. Those companies may not be working for the betterment of humanity, but the ad angle is irrelevant.
Take the following:
> Google+ isn’t about sharing cat pictures, it’s about serving ads. Twitter’s massive network of 140-character bits of information isn’t about connecting people across the globe or to view current trends in worldwide thinking, it’s about serving ads. Facebook isn’t about entertaining yourself with games or sharing interesting links, it’s about serving ads.
Replace every instance of "serving ads" with "making money", and the meaning is unchanged, but the naivete is more obvious. You can do that to the entire article.
Every business is about making money. Whether they make that money by selling ads, or selling a product, or selling a subscription, or whatever else is irrelevant. Making money doesn't mean that a business can't also be connecting people, or organizing the world's information, or curing cancer, or any other fulfilling goal.
> Whether they make that money by selling ads, or selling a product, or selling a subscription, or whatever else is irrelevant
The OP is making the point that, for him, the method of making money is entirely relevant to his sense of fulfillment when working for a company. He does not make the claim that a business cannot be doing lots of other cool things alongside making money - in fact, he points out that Google and Twitter and Facebook are indeed achieving fulfilling goals, but he objects to the income stream and therefore would not feel fulfilled by working for those companies. That's completely fair.
Substituting the claim of the OP about "serving ads" with "making money" distorts the entire message, and of course makes it sound ridiculous.
Then he should just say "I am unwilling to work for a company that sells ads", rather than trying to say that none of Google's work is meaningful simply because they sell ads.
I don't believe substituting "serving ads" with "making money" distorts the message at all. I think it merely highlights how immature his stance is. He stated quite plainly that Twitter isn't about connecting people, that Facebook isn't about sharing links, because they are about "serving ads". The implication here is that a company which sells ads cannot do anything, which is ridiculous. He set up a strawman.
If your interpretation is correct--which it may well be--then the OP fundamentally doesn't understand the business of any of these companies. Relatively few engineers work directly on serving ads. The vast majority work on other things. At Google this includes, but is not limited to, Android, Chrome, search, Google+, Maps and self-driving cars.
Except all those projects are about serving ads. Android is about serving ads on cellphones. Chrome about making browsers better, so consumers will use more Google products, and see more ads. G+ is about harvesting social graph data to serve ads. Self driving cars is so people will check their mail on the way into work, and see more ads.
None of that nullifies the direct value those products provide. If self driving cars mean I check my mail on the way to work and see more ads, it's still a self-driving car. I don't see the problem in staring at a couple of electronic billboards if I can live in the future (and not have to stare at real billboards whizzing past me, for that matter).
The ads are the means to an end, not the other way around. You do what you can to change the world and make a difference, you work on something amazing that you care about, the ads are (often times) your way to fund your ideas while helping other businesses thrive (by bringing in users through buying advertising).
