Greed, yes, but it is absolutely NOT theft. Nobody is reaching into your pants and taking your money then shoving a brick of ammo into your hands. When someone voluntarily participates in a transaction for a non-essential commodity at overinflated prices that doesn't make them a victim of theft. It makes them a victim of their own bad judgement.
I haven't bought 22 ammo since December of 2012, and I won't again until the price and availability is at a level I can tolerate. I also haven't bought any diamonds, gold bullion, Beanie Babies or Ferrari parts. There are guys out there who will compete with each other to pay hundreds of dollars for old model train engines that probably cost $3 new. I don't buy those either.
I think ammo scalping is a distasteful practice and I won't deal with people who do it, but the buyers are just as much to blame for continuing to make the practice profitible. The sellers wouldn't exist without the buyers.
The people I really feel bad for are the ones just getting into shooting, or parents wanting to teach their kids to shoot. Those are the people that scalpers are really hurting. All the rest of us should have been stocked up already.