Imagine, if you will, a pair of headphones. These headphones are the absolute best on the market - the sound quality is superb, they have every feature you could possibly want (and some you didn't know you needed), and they're significantly cheaper than the competition. But, the company that produces these headphones does so by using slave labor.
Is a reviewer of these headphones obligated to mention the fact that they're made by slaves in the review? Should the headphones be given a lower rating because of how they were produced? Should a reviewer recommend that consumers buy a different set of headphones instead, even if the alternative has inferior quality or a higher price?