Nice analogy. Even though it's completely frivolous, and has nothing to do with the basic question that was asked.
However, may I suggest a couple of things. First off, the hundreds of thousands of (professional, as well as casual) off-roaders who DO choose to install snorkels MUST be stark, raving bonkers. And the people at Land Rover, Mitsubishi, Unimog, Toyota, Hummer, Jeep and most of those idiots who build tanks and trucks and APCs and the like, MUST have taken leave of their minds, to have catered for some of their vehicles to come factory-equipped with snorkels.
Secondly, to make an informed opinion on a technical subject, you'd do very well to read up on it, if you don't have personal experience.
Thirdly, allow me to explain using your own analogy. The intake of an engine is through its air cleaner (like your mouth). In most vehicles, this air-cleaner is located within the engine of the vehicle. This intake is FIXED in size. Unlike your mouth, which can open or close, according to the requirement, this inlet will NOT. The temperature within the engine compartment is usually, MUCH hotter than the temperature outside. Now, the cooler the air, the more likely will be the chances of oxygen content in it. The more the oxygen, the better will be the combustion (burning of the air-fuel mixture). The better the combustion, the more efficient the vehicle, in terms of performance, and economy. So as a matter of fact (especially when it comes to off-road vehicles, which have high engine efficiency requirements), without a snorkel, a vehicle is trying to breathe WITH a gas mask on. By providing an outlet to cooler, denser air...the snorkel actually allows it to breathe OUTSIDE the gas mask.
Fourth, a majority of off-roaders will be used for crossing deep water obstacles. The snorkel (when properly fitted, and adequately sealed) raises the air intake to the roof level. This enables the vehicle to be better at fording through water.
On second thoughts, your analogy wasn't really any good, after all.
Cheers.