No matter how powerful a supervillain, his function is to be beaten by the superhero. When that happens too often, the writer needs to increase the threat level if he is to maintain any tension. The best solution is to bring together an alliance of supervillains. So Ian Fleming set up SPECTRE and DC Comics founded the Injustice Gang.

The same logic may be behind Goldman Sachs’ teaming up with Facebook. The only thing they have in common is that they are ideal casting for supervillains. Goldman Sachs is the Darth Vader of international banking, unpopular even by the standards of post-2008 banks, and Facebook’s founder was recently the subject of an amazingly unsympathetic portrayal in a hit film.

It is hard to think of another explanation for Goldman Sachs’ $450 million investment in Facebook – itself based on the bank’s optimistic valuation of the social networking company, which it says is worth over $50 billion.

True, most sector analysts agree that there is still a lot of scope for market growth, and Facebook is now placed to all but monopolise its expanding market. However, if recent history has taught us anything, it is that there are no guarantees in the dot.com business. Facebook was itself built on the graves of Friends Reunited and My Space.

The essential weakness of dot.com companies is that their valuation is often based on no more than wishful thinking. In some cases that optimism proves justified. In most it does not. Customer goodwill is an intangible asset, one that often proves fleeting, even where it really exists.

Some dot.com firms, like Google, have backed up their online presence with more tangible assets, most notably in the form of intellectual property rights. However, Facebook has nothing tangible that justifies anything like that $50 billion price its new best friends have put on it.

So it is hard to fathom out why the usually conservative Goldman Sachs is being so generous. One explanation is that the bankers are betting that Facebook will be allowed to take over other major online players, possibly including Twitter, and are prepared to bankroll the construction of a huge online conglomerate. The other explanation is that there is underground lair somewhere where Lloyd Blankfein of Goldman Sachs and Mark Zuckerberg of Facebook are sitting around a large table with the CEOs of Halliburton, Starbucks, Microsoft, BP, and Disney, plotting to take over the world in the name of evil.

These two explanations are by no means mutually exclusive.