Perhaps it's my training in economics, but I tend to flinch when I hear the word "need". A careful consideration of the nature of opportunity cost renders "need" pleonastic. Its use seems to imply unacceptable consequences of failure to trade. Our pal in the desert needs water in that failure to strike a bargain with Jorge will result in death. I need sandbags for my front door or else my basement will flood. Absent a new anchor, Locke's sea captain founders in heavy weather--he needs that hunk of bent iron.
But daaa-aaad, you don't understand... I neeeeeed an iPhone.
To the economic tin-ear, "wants" are frivolous or selfish; "needs" are simply the unfortunate consequences of this grievous life. Children grasp this and employ the word artlessly, a source of much gentle snickering among the world's parents. Grown adults grasp this too, employing the word with a bit more art, a source of much exasperation among the world's economists. Workers need a living wage, the environment needs stewardship, "we" need to "invest" in "public" infrastructure. The word "need" in many of these cases nixes useful conversations about opportunity cost. Yes, perhaps all these things are useful, desirable, good, but by classifying them as "needs" implies that the consequences of failing to divert resources to them are simply intolerable. End of discussion.
The potential for semantic abuse is clear. Using "need" implies non-euvoluntarity, lending credibility to third-party intervention, whether or not it might be justifiable using careful cost-benefit analysis.
So how to respond to its use? I'm not really sure. it's sort of a trigger word for me. I directly challenge people when I hear it, but I'm a social knobbthicke. Maybe there's a better way to bring considerations of opportunity cost back into discussions. Please share any ideas you might have in the comments section.
I also see it as my parental duty to carefully explain the idea of cost to my daughter so on those occasions when "need" might be warranted, she will know how to use it appropriately. If I end up teaching, it will probably also be part of the first few lectures of the semester.
As for the rest of the time, beware cries of "need". Someone's usually trying to sell you a free lunch.