The military, like any other government agency, cannot allow people to install large religious symbols wherever they want on public property. Once in place for any length of time, those symbols (and usually that means a cross) tend to be seen as established markers, and proposals to remove them are wrongly viewed as anti-religion and, specifically, anti-Christian.
That's what has happened yet again after two large crosses were set on a hill at Camp Pendleton. One was erected in 2003 by Marines who would later be killed in the Iraq war. That cross burned down in 2007 but was replaced a year later. Pendleton higher-ups should have foreseen that allowing the crosses to stay would have led to another one, placed there two months ago on Veterans Day without permission. Now groups that advocate for the separation of church and state are complaining that the crosses should come down, while others are arguing for them to remain as a memorial to Marines who have died.
The cross is widely used in this country to commemorate the dead; in Camp Pendleton, the hill adorned with crosses has become a cherished spot for men and women in uniform to honor their fallen comrades, bringing notes, dog tags and other memorabilia. But the fact remains that the cross is an inherently religious symbol. Those who claim it is merely a sign of mourning, not one that evokes one religion over others, should imagine how they would feel if a symbol of Islam or Judaism were placed on the hillside instead.