The single biggest drawback to profiling or any other systematic strategy is that your enemy has a chance to come up with ways to defeat it. If you know what the border guards are looking for, be something else. If airline security is good, plant your bombs elsewhere. Maybe they won't have much luck finding gray-haired little old ladies eager for 72 virgins, but plastic surgery and disguise can be pretty effective. It doesn't take much to bleach out melanin and defeat screening based on dark-skinned ethnicity.

OTOH, not to put too fine a point on it, security services in repressive regimes have long understood the deterrent power of random action. The population becomes to a large-degree self-governing because people assume that they could be under surveillance at any time. Random security is a pretty good force multiplier--instead of applying to one situation only, your every action can potentially apply to all situations. In the same way you can scare off a mountain lion by puffing yourself up to look larger, random security makes your security service appear to be much larger than it really is.

Ah yes, lessons from the Soviet Union and Nazi Germany...that's the slippery slope that should should scare the beejezus out of anybody who believes in core American values. We survived 9/11, but the jury's still out on whether we'll survive the "Patriot" Act.