Good topic bear,
Yes we whitetail hunters back east have been preached to time and again about food plots. As a biologist, I have a problem with this idea. WAYYYY too many folks think if you dig some ground then plant it deer, especially trophy bucks, will come flocking to your little 25 acre property with its 1/4 acre plot. Bologna!
There's all sorts of good and bad things about plots and feeders. Plots provide more food tonnage than feeders, are legal for all game, give more of a "hands on" approach to deer mangement and as Max said they can also provide cover. On the downside, a lot of yahoo wanna be farmer/deer managers don't have the slightest idea of how to practice good soil management techniques, pick the right seed (which most folks think you have to buy the "deer" blend for $20 more than the livestock blend even though they're the EXACT same thing), or operate the equipment, add lime or fertilizer. Feeders are usually more expensive to run, though less costly to establish, are not always legal and present a vector for disease if not maintained or rotating their positions.
As for the ethics of it. I don't see anything wrong with hunting over crop fields or food plots set up specifically for game. If mother nature will allow it to grow then it's usually more acceptable in the eyes of the game law makers as well as the hunters. Feeders on the other hand don't hold to the same natural laws of weather and soil requirements. Setting up corn in a Yukon mountain range to attract sheep just isn't a natural phenomenon!
Guess my take on it is if it can grow then let it and if deer wanna eat on it hunt them over it. Realistically though when it all boils down, hunting in general uses some form of "bait" if you think about it. For deer hunters, we use scrapes, trails, scents, feeding areas (whether natural acorns, food plots, or feeders) water holes and so on. In my book the more "natural" the "bait" is then the more acceptable it is.