There are many people who claim they didn't use in lube in the "sandbox" or they were taught not to use lube by a drill instructor. These people will tell you lube is totally unnecessary. A waste of money. And, worse, it will collect sand, dirt, etc in the action of the rifle and cause it to fail! The claim is that lubrication will trap particulates, which in turn adds friction to the action and will eventually prevent the various moving parts of the action from fully cycling. This will, therefore; cause jams. Some even claim that too much lube can prevent the gun from functioning of and by itself.
Let me say this as bluntly as possible: this is absolutely ridiculous and completely false. Now, there are some materials that allow a gun to function well without lube, but your standard AR NEEDS lube. Your AR might function pretty well with no lube, but not after hundreds and, certainly, not after thousands of rounds. Dry sand can get caught up in the action of your gun as easily as wet sand - sure the wet sand can stick, but the purpose of lube is to help those particles move out of the way and ensure the action can cycle. But, you don't have to take my word for it:
1. Pat Rogers - Anyone who is familiar with Filthy 14 should know this: a dirty gun, with tons of carbon and particulate build up, after tens of thousands of rounds, run hard, was lubed with Slip EWL the entire time. Why? Because Pat Rogers lubes his guns. And, if you want to claim your experience in war trumps anyone else's experience, he is MORE experienced than you. I recommend you listen to him.
2. Larry Vickers - Here is another prime example of someone with more experience than you. He has nearly 20 years experience as a tier 1 operator in Delta Force. Here, he shows his views on this myth. Again, you don't have to take it from me - you can listen to a legend. Lube is needed for your firearms to function properly.
3. Mr. Gunsngear - He does a great job of showing what happens to an over-lubed Glock - nothing. It runs just fine, but it's slimy. He's got military experience, but he's not trying to beat people over the head with it. He's a good source of information, especially for new gun owners.
The one thing you need to know is that you do have to let the liquid drain out - just like water in a DI AR15's gas tube. If you try to fire most guns with oil in a place where it can't escape from, that's a problem. But, it requires ridiculous amounts of lube to get to that point - more than you would ever reasonably have. And, you know how to prevent that issue? Let the excess oil drain out for about 2 seconds, shake it off, and fire like normal. The myth of over-lubrication is people trying to over-think a potential problem and forgetting basic concepts, such as why oils and lube were invented and used in virtually every big piece of machinery on the planet. It's a trap. Unless your gun has special coatings that can be damaged by lube, make sure there's some in your gun.