It's a game in which people roleplay characters. JUST like actors, the players must thoroughly portray their own characters. If people truly feel that upset about good roleplaying, they probably shouldn't be playing a roleplaying game.
Well, actually, as an actor, your job is to perform a script which somebody else has given to you. If you show up on set, or on stage, and say, "nope, sorry, my character wouldn't do this," you are not doing your job right. Now, if, during the rehearsal process, you speak with the director or the writer and say, "I'm not sure about why my character would say this," or, "I think my character might actually do it like this instead," folks might might be able to work with that to make changes to the script or the play. Sometimes, this is not the case. Ultimately, it is the job of the actor to figure out
why their character would do the things they have been scripted to do, and make that believable.
In a role-playing game, you aren't given a strict script, but you are given a certain degree of a social contract, and it's your job, as a player, to figure out, "why would my character behave in a way that fits within this social contract?" That social contract will vary from table to table, of course. With one of my groups, we like to spend a lot of time figuring out why characters would be working together around certain issues. Player characters have their own individual motivations, and they don't always see eye to eye. My rogue has tried to rob another player character before, while another PC tried to put him in handcuffs. That being said, the actions were taken very much with the idea of advancing characterization and group dynamic. If I had been successful, I think I would have gotten a few copper pieces. Our Lawful Pigheaded Good player occasionally steps out of character to make suggestions about how to "get around" his character's issues.
Other tables wouldn't tolerate that degree of lollygagging, so, at that table, my job would be to figure out how to play my character in such a way that he always showed up on time to the dungeon and played it straight with his allies. Hell, a wizard can put a geas on him if need be.