That is the only argument needed. But, consider also: Scarborough Shoal is many hundreds of miles from the Chinese mainland; the bases for China's historical claims cannot be validated; and Philippine villages like Masinloc have relied on the reef for their livelihood for many generations. China's occupation of the reef is throwing Philippine local economies into disarray.
China needs to recognize that if Italy is the boot of the world then they are the sock. They have no right to try to expand their country. They let their citizens live in poverty and block access to the certain current events in order to keep their citizens uninformed. They don't deserve the Scarborough Shoal.
This seems like a no brainer. According to the United Nations Convention on the Law of the Sea, a country has exclusive economic rights in an area that extends out 200 nautical miles from its shoreline. This area is known as the Exclusive Economic Zone where a country has territorial access of all natural resources (this includes the fishing that China has been doing).
China was a participant and signatory of the Law of the Sea and has ratified it. They have agreed to and were significant participants in these rules.
The Scarburough Schole is located about 124 nautical miles west of the shore of Luzon Province in the Philippines (well within the 200 nautical mile limit).
By international standards, they are bound by these rules and by breaking them, they are encroaching on another countries territorial rights. They should clearly relinquish their claim to the Scarburough Schole.
By constantly violating these rules (both with the Philippines and other countries in the area), they are also showing considerable disrespect not only to the Philippines but also the entire international community and the treaties they have chosen to be a part of. They simply can’t pick and choose what laws they will follow and what they will not.
They must let go of this claim.