They serve food and drinks but the primary purpose for a flight attendant is passenger safety. Their trained to handle emergencies and assist in evacuations. They go through rigorous re-certification procedures annually.
I worked in airline customer service and you have no idea of the kind of complaints we get. A woman complained about the flight attendant because she wouldn't permit her to change her baby in the galley. A woman tried to hand one FA a napkin with doggie doo while she was serving meals and made a complaint, mother got angre when the FA stopped her child from playing with the PA system, a man in the john delaying takeoff. Running up to the gate at the last minute with baggage too large for carry on.
Hundreds more. Being obnoxious and whiney is the least of it. They have to consider other passengers as well. Over the years I've seen passengers become much more unruly and disruptive.
And I've seen and experienced many times passengers percieving rudeness when it wasn't the case at all.

Flight Attendants are not "at your service"" they are ultimately responsible for your health and safety. Bringing you your food and drinks is secondary to your safely arriving at your destination. They are essentially on their feet for hours at a time, sometimes work multiple flights in a 24 hour period and must deal with very
demanding passengers (there is always at least one person who makes impossible demands on them) who think they are on a private flight.

I think people need to grow up and take responsibility for their own behavior.

The passengers are the problem. I have flown over 2,000,000 miles on various airlines and the passengers are far worse than the flight attendants when it comes to being rude and or obnoxious.