What is a single word, or phrase, for something that necessarily causes both harm and benefit? For example, a coal-fired power plant will harm human health through air pollution, but will bring electricity and economic development to a poor area.
Also double–edged sword (M-W) - both versions are equally common on both sides of the Atlantic.
See also it cuts both ways (it affects both sides of an issue equally).
"I think he regards work as a necessary evil."
"Most Americans accept taxes as a necessary evil."
something that, although generally favorable or advantageous, has one or more unfavorable or disadvantageous features.
The word I think I would use would be disjunctive.
It means disjoined, or lacking connection/consistency. So it doesn't immediately speak of both benefit and harm, but if one words the rest of what one is saying appropriately it gives the desired meaning.
Nuclear power has disjunctive effects, both beneficial and harmful.
Maybe no pain no gain. That something beneficial (gain) is unachievable or unreachable without dealing with some harm (pain) as a side dish.
Example: A coal-fired power plant is egregious in a way that one side when it is uplifting the economy of the area, other side it is downgrading the environment.
Already having supplied an answer to this question, it has just occurred to me that the metaphor you may be seeking is * a curate's egg*.
As the Oxford Dictionary Online explains it is British, meaning 'a thing that is partly good and partly bad': this book is a bit of a curate's egg.
ORIGIN early 20th century: from a cartoon in Punch (1895) depicting a meek curate who, given a stale egg at the bishop's table, assures his host that 'parts of it are excellent'.
... if the context is "a bad or unhealthy habit (such as an addiction to smoking)" - Wikipedia.
Smokers are aware of the harm but continue the habit due to their own perception of the benefit.
The closest to a single word we have for the concept would be "catch-22"
It's derived from the novel of the same name.
In your example. "Civic engineers faced a catch-22 when it came to the coal plant. It would allow them to deliver energy cheaply to the area, but at the cost of added pollution"
Word for describing something that causes seizures?
Phrase for something that causes your battery to drain fast?
What is the single word for something that is both lightweight and strong?
Is there an equivalent to "terraform" for other planets?