Better to encourage than force. Throwing charedim in jail will not accomplish anything other than creating a lot of jail kollels.
The IDF should also pay more attention to its own rabbis, and charedi leaders should tell charedi youth that yes, IDF rabbis are orthodox and can be relied upon (and know a lot more about the halachot of army service).
The dati community used to have a huge OTD problem when its young men entered the army. But it realized that the army is needed and it made changes, creating hesder yeshivot and army prep schools. The charedi community should do the same. While many datim are modern orthodox, many others are barely distinguishable from charedim other than dress and the fact that they serve in the army (some in Nachal Charedi!). Concerns are real but they can be worked out if all are willing to work things out.
As charedim become a larger and larger share of the Israeli population, charedim do need to take responsibility for the defense of the country. Otherwise the Arab rashaim will overrun everything and anyone who thinks that torah study will prevent that should look at the example of Eastern Europe in the 1940s.