Just so you guys know. This is not prostitution, this is an old practice called "comforting" and was common in Japan amongst samurai.
A "Comfort woman" is a girl who makes a man feel "comfortable" in a time of war. The main logic behind this is that women believe that by having the birth to a person of noble status this makes them wealthy in status as well.
Whether it be a samurai or a freedom fighter the logic is the same.
I of course am against this as I find it detrimental for any woman to enter into a battlefield for such a purpose. If you want to bear the child of a person with great honor then marry him when he comes back alive. I personally think many of these freedom fighters deserve a wife(perhaps two) for dealing with Assad.
I find this entire practice to be somewhat off to be honest but again, I do understand the thinking behind such women but morally, rationally, religiously or even secularly I find it rather dumb.
If a woman wishes to comfort a fighter then marry him when the war is over or when he leaves the battlefield. Cook, clean and make his days 10x more better. Approach him with a beautiful smile, submissive attitude and grateful demeanor. Marry him and make the relationship binding and THEN you can bear his children.
Until then, this behavior is an assured no no
And this is coming from a kafir!