I haven’t seen a Torah that mentions a chiyuv to join, lihavdil, the State of Israel’s “Tzava”. Maybe the Zionists have a different Torah than the one from Moshe Rabbeinu?
Also, the people who were sent to the tzava were great tzaddikim and Moshe had a way of ascertaining that. We have neither Moshe nor a way of knowing who are “anshei chayil”, etc.
Moreover, we don’t know who is from what shevet, other than kohanim/leviim who know their yichus, so we can’t knos who is from which “Mattos Yisrael”.
Finally, our modern-day Torah sages (Yiftach biDoro kiShmuel biDoro, for ROB) already forbade entering that den of shmad and tumah that is the IDF.
And if that’s not good enough for you, read the stories of people who were spiritually destroyed, them and their families, after going to the “chareidi” units of the IDF, and listen to the Rabbis who are in charge of sending kids to those IDF programs who readily admit that even the chareidi units are not a place for a frum kid.