The Rebbe spoke about this and brought many sources on the matter in Likkutei Sichos vol. 5 pg. 127 fn. 25-26.
See footnotes 25-26 here: https://hebrewbooks.org/pdfpager.aspx?req=14928&st=&pgnum=139&hilite=
Some points mentioned there (I didn’t get to look up all the sources yet, so I’ll just quote as they’re written there):
1. Many Rishonim (רשב”א, רא”ש, ספר החינוך, ספר זכרונות) hold that the mitzvah of לא תסור applies in all generations, not just the Beis Din Hagadol.
ספר יראים argues.
2. Many meforshei Rashi explain Rashi like the sifre – “only if it SEEMS.” However, from the fact that Rashi omits these words it seems like he doesn’t want to be mefaresh that way.
3. Indeed, the Gur Aryeh understands Rashi literally, ימין ושמאל כמשמעו, דאף אם הם טועים בדין – “literally left or right, even if they ERR in judgment.”
See the above link for more sources and discussion on the matter.