The time to warn people about reckless behaviors is NOT when a person is in dire need. It's too late then. We already lost the opportunity to help the person in this way.
Help the person in the way you can, in the moment, and set aside the thoughts about prevention.
These thoughts may be useful for helping other people in the future. Prevention is often more effective and more efficient than rescue and damage control. It is often cheaper and saves more lives. But there is a time and place for it.
When you find yourself having those thoughts like: "You should / shouldn't have done such-and-such thing." set that thought aside for later. Maybe share some educational material later, in a place where people like the person in immediate need might have it reach them, so they don't end up in the same predicament.
But for now, either help if you can, or clear out and allow someone who can, without getting in the way.