There's one reason I believe investors should stay away from Facebook (Nasdaq: FB) stocks. It's the reason Coca-Cola (NYSE: KO), Johnson & Johnson (NYSE: JNJ), and Brookfield Infrastructure Partners (NYSE: BIP) are all relatively safe places for your money, because these companies will probably be around for at least another century.

What key thing do I think that Facebook lacks? A wide moat -- wide barriers against competitors to protect Facebook's future.

What's in a moat
Coca-Cola has an unbeatable brand. Interbrand values it as the top brand in the world at more than $72 billion, and it has an amazing worldwide distribution system that sells to more than 200 countries. (For perspective, the world only has 240 countries.)

Johnson & Johnson has strong brands such as Tylenol, Benadryl, and Band-Aid, and a patent portfolio brimming with potential for continued dominance. Johnson & Johnson's diversified segments -- with about 40% of revenue coming from pharmaceuticals, 40% from medical devices, and 20% from consumer products -- also help protect the company from any shocks.

Brookfield Infrastructure literally owns its moat. It has ownership in 20 ports, more than 3,000 miles of railroads, millions of acres of timberlands, and thousands of miles of natural gas pipelines among its diversified holdings. Brookfield's segments of utilities, transportation and energy, and timber all have significant barriers to entry, and its investors can rest easy knowing its physical assets have real value.

What's in Facebook's moat
Some say that Facebook's hundreds of millions of users represent a significant barrier for others, and because of the network effect each new user makes it that much more difficult for competitors. However, unlike traditional industries, there are few if any switching costs for these users to start spending time at other digital destinations. There are several examples of how easily users can flee from one Internet service and flock to another. One example is the meteoric rise of Pinterest. Another is the downfall of Facebook's previous competitor, MySpace.

Let's look at the case of AOL's predecesor. America Online had arguably a larger moat than Facebook, representing the single gateway to the Internet for customers, while holding their credit card numbers. Switching costs for AOL customers involved more than deleting one profile and filling in another, as they had to find a completely new Internet service provider. Even so, AOL was quickly displaced as new technologies quickly stole users:

Yes, Facebook has more users than AOL ever had, but I would argue that it will be easier for these users to make the next technological leap. Especially since Facebook allows a one-click download for all your information.

A shallow moat with several bridges
Google (NYSE: GOOG) struggles to create a lively social network with Google+, though the company claims 50 million daily active users. However, that number counts any Google+ user who uses YouTube or its search engine as an active user. According to a comScore study, Google+ users spent only three minutes per month on the network, compared with 405 minutes a month on Facebook.

But the bad news for Facebook is that it won't be Google or other established players that create Facebook's demise. It will be the barbs coming from millions of startups, like Instagram. Facebook purchased this upstart photo-sharing network for $1 billion to defend its shallow moat, but it's only a matter of time before the next Instagram rebuffs any acquisitions offers. And unlike potential competitors of Coca Cola, Johnson & Johnson, or Brookfield, Facebook's competitor could be a lone programmer.

The worst part
The next biggest issue is that Facebook's competitive advantage is only one of its many problems. I'll add to the list that some of the problems that other Fools note:

• Facebook membership in North America decreased slightly in the past year.
• Monetizing mobile users through ads, the next technological leap, is more difficult.
• IPOs traditionally underperform the market for three years.
• The low float, or percentage of shares available, will overprice the stock.
• Because of the share structure, Mark Zuckerberg can control the outcome of any shareholder vote.

In short, I don't think investors should touch Facebook's stock. However, the Fool has identified one recent social-networking stock that the market really loved on its first day, and it's a stock our chief technology analyst sees as an even better opportunity than Facebook. To learn more about the one social-networking stock investors should be buying, check out our free research report.