Recent rallies by growth stocks like Apple and Amazon are as much a warning sign as a profit opportunity, writes MoneyShow.com senior editor Igor Greenwald.

Just because the Titanic is sinking, it doesn’t mean all boats are bad. In fact, those little ones circling the stricken mothership become more valuable than ever to the unfortunates treading water.

The reason the S&P 500 still has four digits, given the mess we’re in, is that a lot of people view the stock market as one large lifeboat promising deliverance from the shipwreck of the US economy.

Domestic demand is so weak that people are willing to loan money to a Treasury drowning in deficits for 30 years, for a maximum return that not so long ago would have seemed hardly worth the bother, and never mind the risks. Real GDP per capita in the US has still not returned to 2007 levels, testament to the erosion of purchasing power and bargaining leverage suffered by US workers since.

Meanwhile, the multinationals are minting money overseas, borrowing on the domestic bond market for next to nothing and investing in whatever global project promises the juiciest return. With wages going nowhere, fixed-income yields creeping ever closer to zero and the housing market still on its rear end, who wouldn’t want aboard something so seaworthy?

Retail investors may be running scared, but institutions still seem to be buying equity dips, to judge by the market’s relative resilience.

Parallels between the current situation and the one three years ago before Lehman fell have been all the rage of late, and for good reason.

But I’m seeing more shades of the fall of 2007, when stocks mustered the gusto for one final uphill march, out of the belief that authorities would stop the economic rot before it corroded corporate profits.

One similarity between then and now is the undignified rush into the secular growth stocks, on the hope they will prove immune from the ailments of the broader economy. Because the lifeboat that is the stock market is still wallowing in the Titanic’s turbulence, the passengers are on the lookout for even nimbler, sleeker craft.

Apple (AAPL) and Amazon.com (AMZN) notched record highs Monday because their business momentum may let them ride an economic downturn in relative comfort. At least that’s what the buyers hope.

The preference for stocks with good “stories” and growth prospects is also propelling minnows like Stamps.com (STMP)—the online postage seller getting a boost from the looming wave of US Post Office closures.

The downside is that the economy gets to everyone sooner or later, and stocks seen as “above it all” are liable to get ferociously dunked when macro worries finally swamp whatever feel-good story made investors come aboard.

Apple and Amazon were also at new highs at the very top of the 2007 market, and it took the merest hint that Amazon was, in fact, mortal for its shares to slump 12% from that peak, after a disappointing earnings forecast.

I’m not arguing that we’re at that point now—there are good reasons to believe that both tech juggernauts will continue to steamroll competitors and the few remaining market skeptics for a good while longer. But as the strongest stocks buck the macroeconomic trend, risks rise that the very size of those companies’ market shares will eventually expose them to weaker demand or a new competitive threat.

As for Stamps.com, it’s a decent niche offering might get bought out one day, but in the shorter term it’s likelier to turn into a Netflix (NFLX), and this is not the compliment it would have been three months ago.

That was when Netflix was still perceived to be riding the secular trend of cable customers defecting to its bargain-priced service. Only as soon as Netflix became big it found content providers squeezing it for higher fees, and its attempt to recoup these via higher rates predictably clipped growth, with disastrous consequences for the stock.

Of course, that only happened after the next-to-last fundamental skeptic went broke shorting the stock. The same dynamic seems to be in play for Stamps.com.

The stock has doubled in three months on strong results and an accelerating growth rate. But it remains vulnerable to new competition should the Postal Service’s decline cause bigger predators (hey, why not Amazon?) to seek out its turf. And margins are already pretty thin.

Apple and Amazon are better bets. And while Apple’s valuation seems much more attractive than Amazon’s, both stocks are obviously working out very well as the nicest lifeboats around.

A viable strategy would be to ride both until the first significant dunking on fundamental news, and then to short them just as enthusiastically.