How does this sentence violate the principles of objectivity in writing a summary?

"i believe that common sense presents arguments to convince the colonists of the need to free themselves from british rule."

From the given sentence above, it violates the principles of objectivity in writing a summary because it states more of a subjective opinion rather than basing on a proven idea or statement. The words "I believe" made it appear that it is not objective in a way that it only refers to one's belief and judged according to the speaker's personal view.