"I don't like the word 'gamer' because it's a derogatory term that belittles people as being only that which they do. You wouldn't call someone who reads books a "booker", or someone who watches movies a "movier". So it's stupid to call a video game player a 'gamer'!"
Okay yes, you wouldn't call a reading enthusiast a "booker". Rather society calls that person a "bookworm". And you wouldn't call a movie lover a "movier", but society calls them a "film buff". There was a time in my life when I was keenly into high tech audio, and I admit to having been an audiophile. I'm sure you're getting the point. Throughout our society we have many pet names for people who are very enthusiastic about defined things. "Gamer" is nothing more or less than just another example of this cultural commonality. This being the case, one has to ask one's self why some folks consider "gamer" to be a derogatory term.
Indeed I've read people say merely being called "gamer" supposedly distills their very being into one who only plays video games. This makes no sense. Does anyone really think a "gamer" does nothing else but game? Of course not. That's about as logical as thinking a plumber spends their entire waking life doing nothing but plumbing. Silly thought, no? So if a plumber doesn't mind being called a plumber, a gamer should feel the same way.