“Nothing is useful if it is not useful to man.”
That was author Simone de Beauvoir’s belief in her book “The ethics of Ambiguity”. I personally find it to be true. Real, concrete individuals should always come before abstract ideas.
The first obvious interpretation would be ideals for which people essentially exploit, manipulate and harm each other (for communists it’s a utopia, for capitalists it’s the economy, for terrorists it’s 72 virgins in heaven or something). Whether those ideas can be realized or not, we need to really consider if it is useful to us — and at what cost.
But this also applies to each of us as individuals. What use is money if you can’t spend it on things that work for your well-being? What use is the latest smartphone if all it does it spur you on to get another?
Remember to ask yourself: is it man-useful?