What happened is a Fact. Why it happened is subject to Opinion.
If the person who initiated an event says why they did it, we may teach that as Fact.
It is important that what happened be taught as Fact. We learn valuable lessons from historical Facts.
It is important that Opinion never be taught as Fact. Opinion can shape Facts to suit its own purposes.
When a person combines Fact and Opinion in writing about or teaching History they are teaching you not only what happened but what to Think about what happened.
This is dishonest, manipulative and damaging to the student and hence, Immoral .