Why should you avoid using modern ideas to evaluate a historical event?

Using modern ideas to evaluate a historical event should be avoided because you’re likely to have a lot of cultural bias. Our ancestors and people from the past were not as progressive as we are now and we should not judge them for what was considered “normal” in their days. For example, smoking used to be normal and seen as non harmful. But now we know that smoking kills. If we look back on people in the 60’s who smoked a lot every day, we would wonder how they could be so careless to ruin their lungs but from their point of view, they didn’t know the effects smoking would have on them.