Absolute moronic attitudes displayed by those passengers when their seat numbers are displayed next to their chat lines. It's a simple task of cross-referencing that against the passenger manifest for names, and from there their contact details.
Only thing possibly lacking or needing clarifying for legal purposes is a disclaimer stating that any misuse of the system would result in their entire IFE system to the seat being disabled for the remainder of the flight, and for a cabin-wide CCTV to collect info along with the chat logs to corroborate who was sat where if it then goes to court.
No getting away from that then.