https://www.etzion.org.il/en/halakha/studies-halakha/laws-state-and-society/status-chilonim-halakha-2
The most problematic ruling relating to an apikorus is the law
that he is to be "cast into a pit and not rescued." The Chazon Ish has a
well-known ruling on this matter which is based on the understanding that this
law is meant to achieve certain social objectives:
It
seems that the law of casting [an apikorus] into a pit only applies at a
time when the blessed One's providence is manifest, e.g. at a time when miracles
were common, and heavenly voices were heard, and the righteous of the generation
were under personal providence evident to all, and the heretics were
particularly perverse in turning their passions to lust and wantonness. At that
time destruction of the wicked served as a fence for the world, for all knew
that leading the nation astray brought calamity into the world, and it brought
plague, and warfare and famine into the world. But in a time of concealment,
when faith is gone from the common people, the act of casting into a pit does
not repair the breach, but rather it adds to it, in that it appears to them as
an act of destruction and violence, God forbid. And since its entire purpose is
to repair, the law does not apply when it does not lead to repair. It falls upon
us to bring them back with chains of love, and to stand them in a ray of light
as much as we can. (Chazon Ish, Hilkhot Shechita 2,
16)
The law of "casting down and not rescuing" is meant to repair the
generation, and therefore, at a time when it will not lead to repair, but rather
make things worse, the law is not applied.