Nothing is worse than taking and not giving back, contributing to the community is a crucial jewish mitzvah and value. Some are able to take active service in the IDF others take on positions in organisations such as ZAKA if they feel full army service is not appropriate for them. There are specific charedi army units and amongst younger officers a growing number of frum young people. Some young religious girls find different ways to give back to society be it in standard IDF uniform or other ways of undertaking national service.
Yes Health some do not go into the army, some healthy young men take money from the govt in Israel and stay in Yeshiva and learn, leaving it to others to defend, feed and support them and their families. Others go to hesder yeshivas, learn and defend as well as giving back to society.