To try to make a phenomenon appear good, by comparing it with a worse phenomenon, or to try to make a phenomenon appear bad, by comparing it with a better phenomenon.
Consider junk food. A very nutritionally-conscious person has a rather low opinion of junk food. But what would be your attitude toward a greasy hamburger if you hadn't eaten for three or four days? You can malign junk food because your nutritional standards are high enough to permit you to do so. But an Ethiopian would like nothing better than to have access to MacDonald's, Hardee's or Wendy's and, in fact, such access would be the best thing that could happen to the Ethiopian. Because you have alternatives that the Ethiopian does not have, he is in a position of relative privation when compared to you.
In just the same way, the people who labored in sweatshops at the turn of the century were in a state of relative privation when compared to you. Because your alternatives are different (and much better), the sweatshop seems to you to be an abomination, but in fact the sweatshop was immensely preferable to the alternatives available at that time.
"Eat your carrots! Just think of all the starving children in China."
"I used to lament having no shoes--until I met a man who had no feet."
The real danger from this last example of the fallacy is that if people believe that their own situation really is ameliorated by such a comparison, they will naturally conclude that their own situation can, in practice, actually BE ameliorated by MAKING somebody else worse off! This is what underlies the behavior known as "beggar thy neighbor."
"I know of no assumption that has been more widely and totally disproved by actual experience than the assumption that if a few people could be prevented from living well, everyone else would live better." ... George Kennan
"Misery loves company."
The counter to the relative privation argument when applied, for example, to compare America with other more tyrannous countries is to note that the proper comparison to make should not be between America and other tyrannies but between America and the ideal of freedom.