Are Muslims told to kill polytheists in the Quran?
This Quran verse is often quoted out of context. The preceeding Quran verses inform us there was a war treaty between the Muslims and pagan Arabs, which the pagans of Arabia broke.
Therefore this verse applies to a very specific historical event and applied only to those who broke the agreement.
Naturally, in war violence is expected. If country A declares war with country B because a peace treaty was violated, then both countries will expect their soldiers to kill or be killed.