If you're doing something bad or wrong, there will be two ways that a true friend will react to what you do.
1. Will directly hurt your feelings with his words to try swaying you away from more harm.
2. Will calmly accept what you're doing, give you some feelers that he doesn't like it and that he rather see you do something else. But he will still let you decide on your own and hope that the hurting you will get from choosing the wrong one will make you realize what's bad for you in the end.
But either ways, a true friend will stay with you in the end no matter what. They will support you when you are down. But you should also expect the words "I told you so" from them after that.