[jsbihn]

Ken,
Lets put it this way...
Air filters are designed to keep as much of the outside particles out of your engine. So it filters down the amount that it can let through.
If particles get into the engine they can lodge themselves in various places and cause wear and tear. It shouldnt be the oil's job to filter the particles... since if you get enough particles trapped in the oil it could cause clogging, cylinder scarring, crank wear and so on. Not to mention it also breaks down the oil faster too. If your father believes in throwing the air filter away, then does he also do without an oil filter?
Basically, your father is making the taste of keeping the engine clean harder on the oil filter.

Remember that a car is like a body, and the oil is the life blood of your car. You have multiple filters in your body, but if one of them shuts down you would have all kinds of junk in your blood and feel horrible.... same with the engine

Anyways, to simply answer your question
Are they necessary... No
Should you have one... Yes.