Those who prohibit sunglasses atidim latet et hadin bashamayim . HKBH will want to know why we invented nonsensical sensitivities and obsessed over narishkeit unrelated to Torah. Attaching sunglasses to something the goyim do is utterly ridiculous and insulting to a thinking person and brings no nachas to the Aibishter.
Having said that, I will prove that sunglasses have been permitted by leading poskim.
As you all should know, but as DY has pointed out with hair coloring for men, you don’t and should be forgiven for your am ha’aratzus, there is a machloket between Rav Elyashiv zt”l and Reb Shlomo Zalman zt”l as to the permissibility of wearing lenses that change into sunglasses outside (photochromic lenses) on Shabbat. Rav Elyashiv says “No”,it is Tzove’a. Reb Shlomo Zalman says “muttar”, not Tzove’a. Neither bring up the possibility that Shabbat is irrelevant because even b’chol there is some chashash or other.
Clearly, according to both, it is permitted during the week. Hence, regular sunglasses are permitted during the week and on Shabbat. Hamachmirim will not wear photochromic lenses on Shabbat.