There's two faces to this issue - ethics and legality. Scalping tickets is inherently unethical. The scalper is reselling items without augmenting or otherwise providing an associated service to them. They are purely a middleman. By buying up the finite amount of tickets, they are reducing supply (to 0) to the same demand, creating a sort of mini-monopoly where they hold the power. The band and venue may sell out, but they will never see a dime of this extra value added to the price tag. As far as legality, it is legal to do it over the Internet, but if it's illegal to do it on site, then the law needs to show consistency and crackdown on everyone, especially these greedy corporations, equally.
Scalping tickets, buying them to resale at higher than face value, is the advent of hustler's, whom will do anything just to make a few dollars. This type of activity shouldn't be allowed, as the tickets being sold are a product that someone is selling at what they deem to be an appropriate price.
There are companies and institutions that buy multiple purchases of tickets to sell to consumers at inflated prices. This is unfair to the original ticket sellers, the performers or sporting events, and especially the consumer who was unable to purchase tickets at face value because scalpers hoarded tickets to resell. There are, unfortunately, very few easy measures to prevent scalping while allowing legitimate buyers to sell their own tickets in the event that they unable to attend the event (which is different from scalping).