That's not the situation with the two newer crosses at the Marine base, which shouldn't have been allowed without a plan for a more universal memorial site. One course of action that would allow the new crosses to remain would be to invite Marines of other religious beliefs to add their own symbols to the hill. That would ensure the separation of church and state while also being sensitive to the sense of loss suffered by those in the armed services. It would create a place where all people in uniform can remember the sacrifices made by so many.
Crosses on a public site is the state endorsing christianity. The article does an decent job of making that point. But I think there is a mistake made in that last paragraph where it tries to find a middle ground. Inviting Marines who belong to other religions to display some of their symbols would not "ensure the separation of church and state". It would do the opposite. It would ensure the entanglement of churches and state. It's true that doing so would be an effort to give equal showing to several religions. And that's better than just having crosses. But it would still hold true that the state is endorsing religion.
The way to ensure the separation of church and state would be to actually separate them, or to remove all religious symbols from the public land. The only thing I can see that would be appropriate would be to let the family of the soldiers put whatever they want on their graves. That might technically still be public land. But the nature of the specific grave sites is a private memorial. Thus any symbol would be something that soldier and their family endorses, not really the state.
The cross or any symbol is unnecessary as a way to honor the soldiers. The fact that we set aside exclusive sites for our soldiers is the way in which we honor them. Putting religious symbols up is a way of honoring those religions. And that is the kind of thing the state has no business doing.
I've been to a military cemetery for my maternal grandparents' funerals. They were sufficiently honored without any religious displays. But because they were religious, the speaker threw in some religious words. And that was great because it was a private thing with the family. The whole site was kind of awe inspiring. Just seeing the vast number of sites and the wars they participated in was enough to make me want to honor them. And instead of a religious symbol, there was a huge American flag flying in the middle of the site. That's the only symbol the state needs to be putting on public land.