A couple questions:
1) Does the Torah give a Beis Din have the authority to punish people for private behavior, meaning not b’farhesia?
2) Does the Torah require a beis din to investigate and pass judgment *all* suspected violations of the Torah within its authority (rather than having discretion to enforce where it seems likely to have good results)?
If the answer to either of these questions is “no”, then it would be incorrect to state that the Torah requires a beis din to force people to be frum.