1. Where there is a תועלת not stating the facts would be a violation of
אל תעמוד על דם רעך. However, the listener must inform the person as to how he came by the info.
2. Being מכשיל someone is not necessarily לפני עיוור. If someone else can tell him it is מסעיה לדבר עבירה. As this is a rabbinic prohibition the rules are easier.