Peter's withdrawal was about soteriological status, not social discrimination broadly

Peter withdrew not because he was socially ashamed to eat with Gentiles, but because the circumcision party taught that Gentiles must be circumcised to be saved. Peter's action communicated to Gentiles and bystanders that Gentiles are not really fully Christian. Even Barnabas was led astray. Paul says their conduct was 'not in step with the truth of the gospel' and immediately transitions to discussing justification by faith — not social dynamics broadly. Paul was not against all forms of discrimination in the modern sense; he was against this specific activity communicating that Gentiles are not justified in Christ.