I think that's mainly why most people use expletives: for emphasis or to quickly express their opinion about a topic or person. Which is fine, when you know it won't offend your audience.
We also use them more often when we're trying to motivate an action by engendering an emotional response (because expletives are often triggers for our emotions), rather than create a discussion around the pros/cons of an issue. I think there's a time and place for both approaches to communication.