But who decides who is a rasha or a kofer? That’s the ikar of the issue.
We are all familiar with the Yetzer Hara’s tricks, especially describing nogeia b’davar as l’shem Shomayim.
One of the possible penalties for lashon hara is losing your Olam Habah. Why take the risk? Ask a posek, or at least your rav, before you start publicizing anything.