Great point! If you had a cure for cancer, would you keep it a secret? No! It would be wrong not to share.
Please do not criticize someone for using conventional methods, they may just be like I was years ago, before I became enlightened. That could jeopardize your ability to get through to them. Just offer an alternative approach, one that will save the person money, one that will be healthier for the person's family or pet.
Remember the quote from Samuel Taylor Coleridge: "Advice is like snow, the softer it falls, the longer it dwells upon, and the deeper it sinks into the mind."