A long, long time ago, games had no speech. Most had little to no plot at all. It wasn't until the 8-bit era that games starting getting some plot and dialogue. Games like Final Fantasy were the start of story-telling in games.

The ESRB was around back then, but there was something you probably weren't going to see on the back of the box. Language. Mild or Strong. It just wasn't around, or at least uncommon. I suppose in the more mature games you might see an h*** or a d*** occasionally, but these occasions were rare, and "language" wasn't something little Johnny's parents ever worried about in games.
I'm not really sure exactly when the practice started to take off. It probably was a bit more prevelant during the 16-bit era, and in full sight in the 64-bit. Exactly when it took off doesn't matter. What does, it that did, and that it's sickeningly rampant today. I'm a Christian (as most of you have probably already guessed) and I believe that profanity of any kind is wrong. I'm not going to preach (although I could), but I am going to take this from a secular standpoint, seeing as I might be able to get through that way.
The main point is that language in games is unnecessary. It just is. Take a game like FFVII for instance. I might as well say that I'm still in school, and still under my parents rules. I'll never be able to touch FFVII until I'm out of the house for one reason. FFVII is trashed. Full of language. Which begs the question, "Would I even want to play it even IF I was allowed?" Why, I ask? Why is FFVII full of profanity? None of you can give me an answer. Does some yelling d*** have more emotion than someone yelling darn or dang? When a character yells s***, is is SO much cooler than someone yelling "shoot"? No.

There's really nothing else to say besides that. Look at all the recently great games that've been destroyed. CoD4, MW2, Uncharted, Borderlands etc. Games such as Borderlands would not only chalk your experience full of verbal junk, but add in some "inuendo" as well. Because everyone knows games are so much better when everyone cusses 2 times a second and makes disgusting jokes about the ladies. It's psychotic! The experience is worsened! It's certainly not any better, no matter which way you look at it!

Another way you'd think the devs would look at it, is in the way of buisness. There ARE people who aren't going to play MW2 because of language. But answer me this. Would you NOT buy MW2 because there's no language. Yeah I thought so. That's just the point. There are people who are turned off by games with language, but NO ONE doesn't buy a game because there's none in it. So technically, devs are just losing sales. They might not be huge losses, but they do exist.
If you've read this far, I appreciate it. I hope that I've at least shown you a little bit, that profanity is games in undue in every way. Peace.
-NintendoNaut