I practice Chinese Martial Arts and I want to punch you in your face every time I see you kick with your hands down. You should always have a guard up even when kicking. I under stand the entire tkd argument about kicking with hands down, but from practical sense you putting yourself in big danger every time you kick with your hands down like that. Someone quicker or someone with better timing will lay you out every time you kick.
I'm not saying that what you are doing is wrong for the system you are training in. But in the context of self-defense, having your hands down like that will not serve you well. Keep in mind that many more people take martial arts like Muay Thai, BJJ, MMA than ever before. This means that one day your enemy on the street may actually be skilled. I agree completely with Headhunter about keeping your hands up. Don't sacrifice safe technique for speed and power. Learn to find the balance. Make it a habit.
The joke about TKD that many non-TKD practitioners have is that it's easy to beat a TKD student. Just punch them in their face because we know you'll have your hands down. Even in olympic TKD many of the athletes get kicked in the face simply because their guard was done and never up. Even when they get close enough to put their arms up to prevent from colliding into each other, they don't. They just bump chests and fall off to the side.
If you are going to practice kicks with your guard down then I would recommend depending on something other than kicking to use in self-defense, because the hands down issue will become a habit the more you do it.
