My greatest work I ever shot was in manual mode on manual focus. It was, actually, a blind shot, where all I did was set the hyper focal distance, gauge the distance from lens to subject, adjusted zoom where I thought appropriate, and hit the shutter button. All without looking in the OVF. Is this really cool? Yeah, it was, and I spend every minute bragging about it to someone. But did I do it to look cool? Well, I was all alone in my backyard, taking pictures of a flower while being eaten alive by mosquitoes, so I suppose the only thing I was attracting with my coolness were bloodsuckers. But the fact is, I consider it my greatest achievement not because it was focused perfectly on the flower, not because I had metered correctly, nor was my exposure spot on, but I did it because in that moment, I thought I could. So I adjusted, and went for it. Since then I haven't shot in manual mode again because I haven't been in a situation where I felt the need to use it. Admittedly, I haven't shot anything nearly as good up until now, so hopefully I'll get another chance to try my luck again sometime soon.

If you have the space or the time for thoughts about how cool you look in manual, obviously your thoughts aren't on subject interaction, leading to rather decidedly subpar photos.
Also, standard exposure, like some other people have said here, looks the same in every mode. The difference is in convenience. Do you have the time to consider something artsy like overexposing? Hit that manual switch. Need to take a quick shot before moving on? Keep your finger off the mode switch. Points have been made that once a change is made, it's there to stay. In my experience, this is pure gold, as sometimes there are settings I absolutely do not want tampered with, but in anything not manual these get changed without my say-so. Sometimes I can't have this, but other times I get lucky and my picture, while turning out different from what I had imagined, actually came out looking extraordinary, because what had changed had also changed something in the picture. Sometimes I like that randomness. Sometimes. Mostly I'm just extremely unlucky. :meh:
At the end of the day, however, manual is just a mode. If that's how people roll, let them roll. You'll see later whether they have the skills to avoid the muddy ditch approaching in the distance.