A writer should use the most alive language available. Surely you are aware of what happens to people who go down the path of taking offense at common usage. Now
that's degeneracy they ought to make movies to warn people about.
It's interesting that the nitpickers usually pick on informal language (slang) because that's where language is least encumbered by preconception. To try to reform society by purging usage is like telling characters on TV that they ought to do things differently: the show finished production before you even knew about it (and oh yeah, the characters can't hear you).
Language is marvelously protean. New currents and wellsprings are bubbling up all the time. They're considered ignorant and incorrect until they achieve critical mass. There's nothing to be gained, unless one has the ego of a schoolmistress, from moralizing about this. (On the other hand, I'd say there's a good deal to be gained by stripping down official language in the way that Orwell is known for.) Although I shouldn't be so hard on these people; they make great comedy possible.
By the way, you touched on a hobby horse of mine. The word "gay" is such a fascinating case. It's shifting its meaning again, from "homosexual" to "lame". The sensitive cultural critics behind South Park captured this perfectly in their line, "this is gayer than sex with men". What's fascinating is that this is happening just as our society is becoming tolerant of homosexuals at an astounding historical pace. It's as if the straight world is striking the following bargain: "you can get married, but we get the word 'gay'".