Why are cars with opaque windows allowed to circulate in normal traffic ? One sees such cars everywhere and frequently in France. The same is true in other countries.
The law in France does not forbid tainted windows in cars. If the police issue a summons, the driver can obtain its cancellation by a Judge. Specialist defence lawyers have all this well covered.
However, the law obliges drivers and passengers to wear seat belts when in a car, forbids driving while listening on a mobile phone, forbids having anti-radar detectors in a car, etc. etc.... How on earth can the Police do their job ?
When a law cannot be enforced by a judge, it is a bad law and must be changed.