What is the best way to say in English that 'no extreme is good'? It just doesn't sound English at all.. I need to express that we should seek a moderate solution to a problem and avoid extreme solutions both to the 'right' and to the 'left'.
Seeking a moderate path between extreme alternatives is called seeking a 'middle course' or finding the 'middle ground'.
Note that this saying is more of a positive, expressing the best course of action rather than being the negative expression.
A middle course
NOUN an option or alternative between more extreme alternatives
noun [ U ] UK /ˌmɪd.əl ˈɡraʊnd/ US /ˌmɪd.əl ˈɡraʊnd/
a position between two opposite opinions in an argument, or between two descriptions:
General election: Jeremy Corbyn aims for Brexit middle ground
[This is just a headline, I am not expressing a personal opinion.]
Moderation in all things is the expression whose concept dates back to Ancient Greece (and possibly before):
"Thinkers of ancient Greece held the notion of moderation in high esteem. As early as the nineth century B.C., the historian Hesiod wrote in 'Works and Days,' 'Observe due measure, moderation is best in all things.' The Greek playwright Euripides echoed that sentiment in 'Medea' (c. 431 B.C.) with, 'Moderation, the noblest gift of heaven,' and after him the philosopher Plato advised in 'Gorgias' (c. 375 B.C.), 'We should pursue and practice moderation.' Centuries later, Chaucer first rendered a similar English saying in 'Troilus and Criseyde' (c. 1385) with 'In every thyng, I woot, there lith mesure (moderation or proportion)'.William H.G. Kingston gave the exact wording of the modern version in his translation of 'Swiss Family Robinson' ." From "Wise Words and Wives' Tales: The Origins, Meanings and Time-Honored Wisdom of Proverbs and Folk Sayings Olde and New" by Stuart Flexner and Doris Flexner (Avon Books, New York, 1993). Page 127.
(The Phrase Finder)