I disagree. A friend of mine has a rishta proposal from a guy she was excited about, because he was smart, from a good family, was educated, very well spoken, and had a good job. He seemed perfect.
I also knew the guy and had personally seen him get very abusively drunk. My friends also knew him and knew that he had a drug habit.
Given the level of excitement that my friend had about the guy, me simply keeping quiet probably wouldn’t have helped ward her off.
Sometimes, full disclosure of what you know is best.