From D.A. Carson, on Paul's understanding of when cultural accommodation crosses the line into legalism.

"Paul refuses to circumcise Titus, even when it was demanded by many in the Jerusalem crowd,
not because it didn’t matter to them, but because it mattered so much
that if he acquiesced, he would have been giving the impression that
faith in Jesus is not enough for salvation: one has to become a Jew
first, before one can become a Christian. That would jeopardize the
exclusive sufficiency of Jesus.  read more »