to write an opinion in an editorial in a publication.
to insert personal opinions into an article or statement that is supposed to be an objective statement of facts.
To express an opinion in a news story or a headline. Editorializing in the news columns is not considered good journalism.
To inject the opinion of the writer in a story.
An "editorial" in a newspaper offers the collective opinion of the newspaper's management on a topical issue. Writers "editorialize" when they offer opinions on a subject of topical interest. Unlike the approach of an argument, editorializing writers do not always consider the viewpoints of their opponents.
To express opinion towards a news story. Editorials are properly confined to the editorial or Op-Ed page or to signed columns elsewhere in the newspaper.