It's important to remember that parrhesia (frank speech) wasn't just used with philosophical adversaries or people the Epicureans disagreed with. According to Philodemus's work, it was a tool of instruction within the Epicurean community. If someone wasn't living up to their potential in putting the philosophy into practice in their life, the teachers would engage in frank speech to correct the student.
I keep meaning to read Voula Tsouna's The Ethics of Philodemus cover to cover which includes a section on this (and to try and get ahold of Philodemus's On Frank Speech). I've mostly used Tsouna's book to harvest citations and excerpts from Philodemus.