What is the main advantage of having a curtain at the main cabin door in CRJ aircraft?

Having a curtain at the main cabin door in CRJ aircraft primarily enhances passenger privacy. This feature creates a physical barrier that helps to minimize the visibility of the cabin interior from the outside, allowing passengers to feel more secure and comfortable during their flight. By blocking the view of the main cabin, it provides a sense of seclusion, which is especially beneficial during boarding, deplaning, or when passengers are settling in.

While it's true that the other options address various aspects of cabin management, they are not the primary function of the curtain. For instance, safety during takeoff is more closely related to structural features and procedures than to a curtain. Temperature control is typically managed through the aircraft's environmental control system rather than a curtain. Separating classes of service is a relevant consideration as well, but the curtain's primary aim is to enhance privacy rather than divide service levels. Thus, the curtain serves primarily to improve the overall passenger experience by fostering a more private environment.