Businesses that rely on and grow from network effects, die from them too at an even faster rate. A scandal or rival product could take FB to zero. Some would say that history tells us it is FB's inevitable outcome. I know some believe that it can't happen and the FB is "the last social network" but that sounds a little bit like bubble participants claiming "this time its different".
The warning signs of FB rising were apparent for years, but the News Corp managed MySpace did nothing to curb its rise.
As such, Facebook takes all the profit from social media advertising, and can set its own prices and dictate terms to its customers. Ford can afford to do no such thing.
If Ford were the only auto maker in the world, it would be a far more lucrative investment.
ExxonMobil is just oil. WalMart is just department stores. Visa is just credit cards. All those companies have top-20 valuations. It's possible to come up with a doomsday scenario for any industry ... but by and large, once they get really big, they tend to persist in some form.
It is only this year that internet advertising is projected to match TV advertising spend. TV advertising has been around ~50 years, and before that we have another ~100 years of print advertising to learn from.
From those historic precedents we can see that advertising is a huge, huge market. It is true that something could surpass internet advertising as the best way to spend that money, but I don't see any viable candidates (I'm including mobile & VR ads in "internet").
AdBlockers - of course - accelerate the trend of the money in the "internet" category going to players like FB where they control the delivery mechanism (ie, deliver ads in a mobile app, where an ad blocker can't reach it on most platforms).
To me, Google and FB's PE ratios are sensible, taking into account current profits, continuing growth in the short and medium term, and uncertainty in the long run.
Your "Creating the Product" and "Generating Demand" elements synergise off one another. Facebook has considerable network effects, and those network effects stimulate content, but break the chain, or boil-off customers (see "The Evaporative Cooling Effect"), and the feedback's strongly negative all the way down. MySpace imploded quite rapidly. Google's G+ had some traction initially, but worked exceptionally hard to drive off its strongest fans. Those who are slower to learn (/me raises hand) are only now being convinced of our error.
But "Obsolescence" is the big one. Ford's plant degrades from the inside, and the rate of amortisation of manufacturing equipment is fairly well known. Innovation in automobiles peaked in the 1920s, though it's arguable that there were additional spurts in the 1970s (largely around economy), 1990s (quality and electronic controls), and now a possible shift to hybrid or electric vehicles, though those remain tiny portions of the entire market (highly visible, but still tiny by either unit count or, slightly less so due to much higher per-unit costs, currency marketshare).
Ford, along with other US automakers was blindsided when a very modest amount of market innovation, toward more efficient vehicles, hit in the 1970s. That was an exogenous obsolesence function.
Facebook and other technologies face this all the damned time. As I've slowly realised, the cost of provisioning technology hardware falls by an order of magnitude per decade. The rate is much slower for software, but there's far more capable, far more modular software rising up all the time. You can actually see this progression going back to the dawn of electronic computing, with IBM owning the market in the 1950s and 1960s, then a cascade of first minicomputers (DEC, Wang, Sun), then micros (PCs), then laptops, now handhelds, coming along at roughly 10-year intervals.
Software's taken a while to catch up.
Facebook had roughly 1/10 the hardware cost profile of Google (though growth of the Web may have increased that). Scaling out a startup now is largely a solved problem. Revenue model is harder -- but you need far less revenue.
The other problem Facebook (and any other tech player) faces is that their own codebase becomes liability. For every table-based desktop site (say, Hacker News), that existing site layout (and perhaps much the technology underpinning it) actively impedes movement to mobile or tablet devices. I've had long arguments with designers of sites who insist on pixel- and point-based font sizing, rather than em and rem, and then screw up with low-contrast sites to boot.
(HN's own fonts are barely readable for me on a 10" tablet, and no, mobile extensions don't help.)
Further, "Making Money" for Facebook has been exceptionally reliant on both easy-money Federal Reserve policies, and lending and banking regulations favouring Silicon Valley style investments. A tremendous amount of advertising is itself financial services, electronics, and other startups (I'm basing this off of Google's advertisers which I'm familiar with from other sources, but suspect FB's profile is similar). That ads money could well dry up damned quickly.
Tech companies have the problem that as the money dries up so does their tech workforce. Look at the salaries reported to have been offered to Yahoo's top tech talent (if you can't offer appreciating stock, you've got to bleed money). Lose programmer interest, and again there's a downward cascade of talent and capabilities, and some of the negative feedbacks start dominating.
CREATING THE PRODUCT: Facebook's engineers provide the framework, but each day's content is created free of charge by 1.5 billion active users. That's great for profit margins! At Ford, cars don't get built unless the company buys steel, glass, tires, etc. and pays workers to put it all together. That really squeezes margins.
GENERATING DEMAND: Facebook's users share content and invite their friends to join, at no cost. Media companies beg to play in Facebook's ecosystem. By contrast, Ford needs to spend billions on advertising to get people excited about cars.
OBLIGATIONS TO CUSTOMERS: Facebook has a modest-sized fraud and security team that keeps everything tidy. They do heroic work, but there aren't 50,000 of them. At Ford, the requirements for inspections, safety tests, recalls, legal settlements when vehicles go bad, etc. are vastly larger.
OBSOLESCENCE: Ford has $58 billion invested in plant and equipment. Every day, those factories get a little closer to being obsolete. Ford must constantly either raise cash or reinvest profits to keep its factories competitive. That means less free cash for shareholders. By contrast, Facebook has just $8 billion invested in server farms, beautiful headquarters, etc. Its asset-maintenance burden is vastly less -- and should stay that way forever.
MAKING MONEY: Ford's net income zigzags all over the place, jolted by lots of market/economic issues. Net income was down last year; historically it's ranged from $11 billion to sizable losses. Facebook's net income totaled $3.7 billion last year and is climbing at a very snappy rate. 35% a year? Doubling? Still hard to tell, but it keeps going up.
Put all those factors together, and Facebook is a growth stock with a pretty straightforward path to making its business hum. Ford is a cyclical stock that may have already posted its peak profits. Ford may be a bedrock part of the U.S. economy, but that doesn't always get you a lot of love in the stock market, for reasons above. Yeah, Ford has $150 billion in revenue a year and Facebook had just $18 billion. But markets value companies on their growth prospects. I've got no trouble believing that Facebook's overall opportunity to make money is 6x better than Ford's.