Full Idea
For Protagoras the only constraint on human behaviour is that it not interfere with social harmony, the essential condition for human survival.
Gist of Idea
For Protagoras the only bad behaviour is that which interferes with social harmony
Source
report of Protagoras (fragments/reports [c.441 BCE]) by David Roochnik - The Tragedy of Reason p.63
Book Reference
Roochnik,David: 'The Tragedy of Reason: the Platonic logos' [Routledge 1990], p.63