Rav says that this leniency applies only if they have not made an eruv. However, if they did, this leniency is not needed: at the very least, people can take things from their houses into their own courtyard, and this is enough.
However, Shmuel could not understand his reason: if all roofs are one area, what does it matter if the people made an eruv (common food) or not? Rav Chisda explained that either position has its problems. If we always allow carrying things in the courtyard, just like Shmuel said, people will be utterly confused: things that started Shabbat in a courtyard can be carried to another courtyard, but things that originally were in a house cannot!? Now different things have different laws for carrying!
However, this indeed may be the case, according to Rabbi Shimon. Rabbi Shimon trusts people's intelligence and believes that they won't be confused. In fact, there was a similar case of three adjoining courtyards where the law depended on which courtyard the object came from, and Rabbi Shimon did not make any additional precautions.
Art: View Of The Roofs Of Paris by Vincent Van Gogh 1853- 1890