Come on Joseph, do you really not see the difference between firefighters and soldiers? Yes, firefighting is a dangerous profession, but there is a difference between a fire which, while dangerous, is not actively seeking to kill and destroy as it is not a living conscious being. As opposed to our enemies who would like nothing more than to kill us all if not for the soldiers standing between them and us.
But that’s not the point. The real reason we don’t have a mi sheberach for firefighters is because one wasn’t composed and accepted as part of our tefilah. But one does exist for soldiers and it’s a tefilah that is meaningful and emotional to much of Klal Yisroel. By trying to logically explain why their emotional tefilah is unnecessary is hurtful and offensive and I’m sure you could probably think of a less upsetting why to explain why your kehilah doesn’t say it without minimizing those who do say it.