If you hold Lev Tahor has a din of rodfim (which is very likely true) and Ami is protecting the rodef from carrying out it’s evil then Ami has joined forces with the forces of evil.
This is more than just your typical “I think your shita is krum”. We are discussing evil individuals harming others both physically and spiritually. In such cases, it is not lashon hara if everyone must do what is possible to stop them.