I have one. Why did I get it? Honestly, I was waiting for a friend who was meeting me for lunch, and he said he was running a little late, so I figured I'd amuse myself by getting it done.
I don't have a sexually active lifestyle, so THAT reasoning is BS. No one sees it, so it's just something for me. I'm academic, so I can't do anything too outlandish because I have to maintain some professionalism - so I keep my tattoos and piercings in places that are hidden from general sight.
I love it. I love the freedom to be able to do what I want with my body. And ironically, it healed faster than any other piercing or tattoo I've ever had.
I have to disagree with you on a few things. It was the least painful piercing, if you have it done through the middle of the tongue then it's going through tissue, not muscle. It doesn't chip your teeth, I've had mine for 5 years and my teeth are fine (at one stage I had 3 tongue piercings, one behind the other). Also if you have your nipple pierced or even belly button it's not on show all the time so it's not always about what people can see, I just liked it and got it done. Finally any piercing can get infected if my looked after properly, a long as you have good hygiene then there's no reason why you would get an infection x