Nowadays, more and more people are able to fly. With the advent of low cost carriers, air fare have been getting lower throughout the years, hence, allowing more and more people to ride airplanes. Apparently, some think that riding an airplane is just like riding a bus, which is why they take safety and proper etiquette lightly without realizing that safety is paramount for every airline.
Why is this so? Because you simply agreed to their Conditions of Carriage when you purchased your plane ticket. In other words, you subjected yourself to the airline's rules and regulations which are actually approved by a country's governing commercial aviation laws and policies. So if a flight attendant tells you to take your seat and to fasten seatbelts when the seatbelt sign is on, you have no choice but to follow.