It's not trivia and it's not limited to violinists. It's a big issue for lower pitched instruments, and affects woodwind, brass, and strings. It's only 'not' an issue if you're unaware of the differences. Violins, violas, and cellos tune their strings to perfect fifths not ET fifths. Basses are tuned in fourths.Doesn't matter. The difference is well within the margin of error of your ear. Let the violinists fuss over that bit of trivia.
Since in the modern era of easy access to recorded music most people are only exposed to equal temperament, they are less aware of how out-of-tune it can be. ET is a compromise designed to enable keyboard instruments to be more-or-less in tune regardless of what key they are playing in. Fretted instruments like guitars are mostly set-up (fret positioning) to play ET as well for the same reasons.
It's much more critical with small ensembles like wind/brass ensembles, string quartets, viol consorts, or in close harmony e.g. barbershop, as that's when the tuning issues are more apparent, especially the major third. A chord sung/played where the notes are in 'just' tuning really 'pings' in a way that an ET one doesn't.
