Yekke,
1. On the contrary, joining the IDF is avodat Hashem.
2. On the contrary, much has been written. The Tzitz Eliezer wrote a set called “Hilchot Medina”. Rav Herzog wrote several books. There have been many articles in “Techumin” and other Torah journals.
Lilmod, fighting our enemies is a Torah obligation. So is engaging in civilian rescue (e.g. people who get lost while on tyulim). While there is much that needs to be fixed (including in each one of us) there is much that is done according to Halacha. In fact, Rav Asher Weiss mentioned in several shiurim that he receievd questions from the IDF that were relevant to the shiur.