I've been thinking about this question. Here's what I've come up with:
Soldiers are men who are trained to fight and kill, and also to be prepared to die for the cause the leader sets them to. They were coming up to fight a kind of war ("come back as slaves to Egypt or die") of sorts against a crowd of people who were not soldiers, nor very likely able to defend themselves. Basically, God fought the Egyptians on behalf of the Israelites. Another army could have stepped in to fight the battle, and we would most likely not mourn about Egyptian losses. If you die by sword or by drowning as a soldier, it's still the same fate of death--a hazard of the job.
Sometimes God's eternal messages are painted on an "epic" canvas: "When God rescues you, even when the enemy tries to recapture you, you are safe; and God gives grace even when you have fear."
...But, then there are always other questions that can be asked about other battles that were fought under different circumstances. Some of them are more difficult to "comb out" than others.
One thing I've discovered is that when I get a lot more background info, I can understand the reason why a battle was fought.
Another thing is that sometimes we think that the Bible promotes all the actions of all "good" characters. But that is not necessarily the case--the Bible sometimes reports some things without comment, at times. Some of these things are NOT good, such as certain events in the times of Judges, or before the exile; or of certain characters, like Judah and Tamar.
I am a parent, and I think most parents know that there are times when we do/allow something that looks quite unfair from the point of view of the child. We often get accused of being unjust, even as we try to train our child to respect justice. Unfortuanately, there ARE times when I am unjust, because I still do sin. But God is perfectly just, and there is sometimes a question if He is being fair, since we don't see all the info/see into hearts like He does.
At this point, I always remember the incredible death of Christ, and I think, God knows justice; God knows mercy. God knows these things better than I do, and if His character is like this, then I can trust Him even when I don't understand everything. (And, it is still okay for me to try to learn answers to questions like these, too.)
bebu