While some philosophers may disagree with me, all statements made by an entity with agency contain the implicit prefix "I believe that..."

In terms of rhetoric, explicitly adding "I believe that..." to the beginning of a statement softens the statement to a degree that the speaker may not desire. When a vegetarian holds up a sign saying "Meat is murder" I don't think very many people are confused about "according to whom" or that they think the person waving the sign believes that killing animals is actually against the law. "I believe that killing animals for food is immoral and unjustified so we should stop" certainly lacks the punch of the original statement, and the number people who are confused about the original statement is small enough to justify the punchier language.