His parents said this because they were afraid of the Jews. For the Jews had already determined that anyone who confessed Jesus as the Christ would be put out of the synagogue.
Textus Receptus (TR) - John 9:22 >Ταῦτα εἶπον οἱ γονεῖς αὐτοῦ, ὅτι ἐφοβοῦντο τοὺς Ἰουδαίους· ἤδη γὰρ συνετέθειντο οἱ Ἰουδαῖοι, ἵνα ἐάν τις αὐτὸν ὁμολογήσῃ Χριστόν, ἀποσυνάγωγος γένηται.