If you can't say something to someone's face, you shouldn't say it on social media either.
If you can't say something to someone face to face, it's probably not a good idea to say it on social media either.
この場合、次のような言い方ができます。
ーIf you can't say something to someone's face, you shouldn't say it on social media either.
「面と向かって言えないなら、ソーシャルメディアでも言っちゃだめ」
to say something to someone's face で「人に何かを面と向かって言う」
ーIf you can't say something to someone face to face, it's probably not a good idea to say it on social media either.
「面と向かって言えないなら、ソーシャルメディアで言うのも良いアイデアではないと思うよ」
to say something to someone face to face で「人に何かを面と向かって・差し向かいで言う」
ご参考まで！
カナダ 
