Miley Cyrus -- BASHED For Covering Zeppelin/Baez Classic

Miley Cyrus already offended boomers across the country with her Beatles cover ... now, she's going a step further with a Led Zeppelin/Joan Baez classic -- and people are pissed.

Cyrus recorded "Babe I'm Gonna Leave You" -- re-naming it "Baby, I'm Gonna Leave You" -- and posted it on Soundcloud Friday. Judging by the comments ... not well received.

Some highlights:

-- "Further proof that Gene Simmons was right - rock is finally dead."

-- "Thank you for destroying my favorite Zeppelin song."

-- "When my dog farts it sounds better than this."