It's not just the manufacturers who are responsible for the gouging, it's the kosher distributors. Here in Minnesota, despite a good sized Orthodox and Conservative kosher keeping population, the single distributor of kosher foods jacks up the price of staples. If you can find Fleishman's parev margarine NOT supplied by this middleman, the price is reasonable. Find it in "kosher" section, it's twice as much. Wars between glatt/non-glatt and other special interests only serve to heighten the mark up. As for the tzedek part, Torah commands us to treat both our "servants" and our animals fairly. We already know how some manufacturers treated theirs. In this day and age, humane treatment should not have to be an issue.
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from the article: The cost of keeping kosher