It is amazing how people can manipulate facts to convince others with things that without this manipulation would have been considered normal and even the only acceptable attitude.
The verse says:
" Believers, whenever you encounter a hostile force of unbelievers, do not turn your backs to them in flight. For he who turns his back on them on such an occasion - except that it be for tactical reasons, or turning to join another company - he shall incur the wrath of Allah and Hell shall be his abode. It is an evil destination." (8:15-16)
The verse orders Muslims NEVER to turn their backs to their enemies in war. A Muslim is allowed to turn his back to the enemy only in case of tactical reasons of war or to for example seek reinforcements or join another party in the rear.
What the Qur'an does forbid is disorderly flight produced by sheer cowardice and defeatism. Such a retreat takes place because the deserter holds his life dearer than his cause. Such cowardice has been characterized as one of those major sins which, if committed, can be atoned for by no other good deed whatsoever.
This has been declared a deadly sin because in addition to being an act of sheer cowardice, it demoralizes others and can generate demoralization which can have disastrous consequences. An individual soldier's desertion might cause a whole platoon, or even a whole regiment, and ultimately the whole army, to take flight. For once a soldier flees in panic, it is hard to control the others.
How could this verse be considered violent when it is ordering soldiers in a war not to act cowardly. Is it normal for a leader of an army to order them to run when facing the enemy? If he did, will you consider him a good leader then? strange logic desperately trying to justify false accusations.