I think that papers and researches ought to be authorshiped by more than one, two or even three authors.
Scientific research requires cooperation and tasks arrangements and team work.
As for one author paper it may be a review or scientific opinion from an expert in a specific field and this expert author ought to be pioneer in his field to the degree of being a super nova mega star if this term apply here.
Papers belonging to randamized controlled trials (RCTs) are usually blinded and such blindness in the paper methodology are impossible to be done by one author unless the blindness is from the participants side not the investigator side.
In philosophy, single author papers are the norm. Philosophy papers generally have the form of an argumentative essay rather than a report. Given the critical nature of the discipline, it would be rare to achieve a "meeting of minds" on all the aspects of a topic that are expounded in an article. If there is coauthorship, it tends to be in technical or formal areas of philosophy such as symbolic logic.