It doesn't really matter what they were doing, having been soldiers is irrelevant.
Regard for the dead is really regard for the family and friends.
It matters to them and they have emotional needs surrounding the disposition of the body of their dead loved one.
In the case of next of kin, there is ownership too.
However, there are situations where accommodating this ideal isn't a practical reality.
There would be compromises like mass spreading of ashes, or mass burial of
asses 
ashes.
But burying in a land-fill is just too much.