Here's my take on this:
Use what works for your book.
It seems easy enough, right? It's not - at least for many authors.
You see, authors tend to put themselves into their books. Sometimes, this is great, because it means that we can get honest reactions to situations. I can totally imagine some of my authors sitting at their computers running through scenarios from start to finish: If someone walked up behind me and goosed me, what would I say? How would I react? Would I scream? Would I jump? Would I simply keep walking?
But - and this is a big but - the question truly should be: If someone walked up behind my character...
And this makes all the difference.
Probably the most obvious place this happens is with interjections. (In case you don't remember what interjections are, I offer you this from Schoolhouse Rock.) (And even if you do remember what they are, this is kind of fun.)
You can tell a lot about an author when you find that the interjection doesn't match the character.
When the "gotta stay gritty" author has an otherwise suitably grandmotherly character yell out "Fuck you, you asshole!" at the pizza delivery boy who handed her the wrong pie, readers might suspect something is wrong. On the other hand, when the author who doesn't like to get too close to things has her college-age ruffian say "Gosh, that's no good," readers will probably also get the feeling that something is out of place.
For fiction (or memoir, for that matter) to really work on all levels, your characters - and your audience - should have as much of an impact on your word choice as your own personal opinions do.
It's not just in fictional outbursts when words have meaning, though. You only have to look at two or three different news sources these days to realize how much difference word choice can make.
When one news source says "passionate young men chanted as they processed through town" and another says "domestic terrorists shouted out epithets while carrying torches and storming through town" - both trying to describe the same situation - you can start to see the power of words.
As writers, we create the world that our readers will see. In fiction, this can be a fun, playful task - or a painful, laborious one - depending on how well you understand your characters. In non-fiction, this takes on even more weight, since - in essence - you're crafting the world your readers live in.
As readers, we need to hold authors accountable for their word choices. If a character's words don't match the character's character, it's up to us to decide if we should read on.
If what we're seeing with our own eyes doesn't match what we're being told, we need to call the author (or news organization) out.
Words are tools. Use them wisely.