Um, yes time does change what is good and what is bad. That is what time does, changes things. Fruit for example changes from being good to being bad over time. Our opinions as a society change the concepts of what is good and what is bad based on the passage of time. Something that was once perceived as bad can be perceived as good all based on the passage of time, and vice-versa.
Again these are not rules written in stone, but rather written in pencil. Techniques change based on experience over time.