With all the Battles that were fought in the OldTestament not one person ever identified as a ConscientiousObjector.   

What conclusion can one draw from this?   
That a ConscientiousObjector cannot claim Biblical reasons for their objection.   

So, where does the idea come from?   
The Liear Satan who is the father of Liars.   
Satan always uses a little bit of truth to make his Lies palatable.   

"Thou shall not Kill".   "Do unto others...".   "Do good to them that hate you".   

Since God sent Israel into Battle it is clear that "Thou shall not Kill" is intended to prevent Killing for selfish reasons.   

In the same vein "Do unto others" is intended to reduce the amount and extent of selfish actions toward others.   

You ought to "Do good to them that hate you" by sharing the Gospel with them.   

So, you see, using the above cited Scriptures to justify being a ConscientiousObjector requires twisting them to suit one's selfish purpose.   

At the heart of a ConscientiousObjector is a Selfish Coward who may in all other respects be a perfectly fine person.