I don't disagree that people need to avoid tobacco and alcohol as much as possible if they want to avoid cancer. But I don't think that this topic is as simple or straightforward as it seems.
There are people who get cancer despite never smoking or drinking. And there are people who do both and never get cancer. There is clearly a strong hereditary factor when it comes to cancer and those with the genetic inclination for it will probably get it no matter what.
Having said that, at this point in medicine, there is no clear way to know which group people belong in. The only indicator is family members who have had cancer. So it's best for everyone to take their precautions, stay away from bad habits and try to be as healthy as possible. I just wanted to clarify that there is never one single cause for cancer. It's always a combination of various factors.