It's not only men who dislike the idea of female combat troops. Here's an article on the issue by an American writer, Kathleen Parker.
Her argument against female soldiers is that men and women aren't equal in all things, with men having greater physical strength and endurance than women. This is a good argument, but too limited. A liberal could reply that women could serve as soldiers in areas where technology has done away with the need for physical strength.
What Kathleen Parker needed to do was to go on to talk in greater depth about the differences between men and women. That, for instance, most societies value women for upholding gentler feminine qualities of love, kindness, forgiveness, empathy, charity and physical grace and charm. And that men who see the goodness in these qualities respond protectively, so that societies value qualities in men appropriate to the protector role, such as courage, strength, perserverance, honour, loyalty and so on.
We instinctively feel it to be wrong when women are trained for combat, firstly because we feel that it's central to masculine life to want to protect women from harm on the battelfield, and secondly because we don't want the gentler and finer qualities of women to be brutalised by battlefield conditions.
It is a kind of outrage to our self-identity as men and women to deliberately send women to either kill or be killed in warfare.