It's an unfortunate situation, but you cannot blame the airline for your failure to determine what documentation is required to enter a country. It is
always the travelers responsiblity to have the correct documentation. French citizens require a return ticket, as do all other EU, Canadian, and U.S. nationals:
Passport required
Return ticket required
Visa required
Australian
Yes
Yes
No
British
Yes
Yes
No
Canadian
Yes
Yes
No/1
Other EU
Yes
Yes
No/1
USA
Yes
Yes
No
Passports
To enter Argentina, a valid passport is required by all nationals referred to in the chart above. The passport must be valid for at least six months beyond the date of departure from Argentina.