It counsels Perdiccas to respond to this objection by saying that Plato was born when his fatherland had already been corrupted beyond the ability of his counsel to benefit it, while the risks of engaging in its politics were great, and that he would probably leave off counseling Perdiccas himself if he thought him incurable.
The passage advises Perdiccas to respond to this criticism by saying that Plato was born into a world where his homeland had already been irreversibly harmed, making his counsel useless, while participating in its politics carried substantial dangers, and that he would probably stop advising Perdiccas if he considered him beyond redemption.