No military is a democracy. No military can afford to have common soldiers, noncoms and junior officers deciding which legal orders they will obey and which ones they will not. When attendance in an on-base event is mandatory, that means the individual has no choice but to attend. This is a case of "the camel's nose under the tent flap". In addition, the business of women singing is NOT halakha, but minhag (custom, not law). The only thing a soldier so adamant about not hearing a woman sing is to request guard duty at the time of the event, thereby legitimately excusing him. End of story.
Web campaign raises $67,800 for Syria refugee family in a day (Reuters)