smoking cigarettes
Nobody got the Nobel Price in medicine for showing that smoking causes cancer because of the way the authorities dealt with the issue at the time that discovery was made.
The current policy of requiring warning labels on cigarettes doesn't seem to be very evidence based and might cause more harm that it's useful.
avoiding healthy food
That's beginning the question. Different people have different opinion of what's healthy and when you read a bit on LW you will find that plenty of people agree with the official canon.
exercise
That's also a pretty broad category.
Instead of doing your three times 30 of jogging per day and sitting in front of your computer it might be better to get a walking desk and damage your ankles by jogging.
It's not quite clear that the current philosophy of what exercise is supposed to be is optimal.
You're missing the point. "Authorities are always wrong" is not only demonstrably false (I could have listed a dozen other examples), it practically invites the reader to think that reversed stupidity is intelligence. We follow the wisdom of the majority because we don't have the cognitive capacity to reason through every problem as if it were new, and by doing what the majority does in scenarios where we're not domain experts, we're at least guaranteed a "not-terrible" outcome, even if it's sub-optimal.
Another month has passed and here is a new rationality quotes thread. The usual rules are: