Katas arn't meant for Duelling. They are a special move that requires a Jedi to use some of his Force points to perform a series of powerful swings in order to dispense of multiple targets at once, or at least cut down on the number of threats in your given area.

As for the "Barrier", if one is open minded, one will see that the name of this Kata is adequate to what it is meant for.
The Jedi uses the Force to make his Lightsabers fly around him, thus creating a "Barrier" from his opponents, if anyone attempts to cross this barrier, they are severely damaged, or even killed. You seem to think that the word "Barrier" should mean "It protects you from everything".

This is quite simple - Targetting.
It very easy to 'miss' with a Kata, so the developers enabled turning while performing them so that a player could better target their enemy while performing it. Now, seeing as most Katas involve the player moving forward, it would be very easy for someone to dodge it and attack you from behind while you were performing the move. Being able to turn while performing them is just meant so that a player doing a long kata can have more control over it and move to where his/her opponent is.

That was never my point. I have no doubt that a Jedi could use the Force to make his Lightsaber spin very, very fast.
My argument is realistic, Jedi duelling. It's real time, strategic fighting, not "Spin around manically untill something dies".

You have clearly never been in a FFA where you are working really hard to stay alive, working for your frags and having fun, when a guy comes in with Duel Lightsabers, jumps right into the crowd of people, does the barrier+spin and takes out everyone in the area. And not just once either, they'll run off, wait for everyone to gather again and do it over.
It ruins the fun of a FFA, it annoys alot of people and lastly, it is using an exploit of a system set into the game in order to kill people with one hit - which was never intended to happen. A complete and perfect RDFA won't make a one hit kill, and that is a special move for the most powerfull saber style in the Game. So why should there be a one hit kill for lesser saber styles? It just makes no sense.

Personally, I would rather you stop using it completely, but I cannot control what you do in your own time with your friends. But just be warned that such exploits disgust me and many other people, if you are seen to be practicing exploits, you will lose the respect of many, many people, including me, for what it's worth.

Why should one type of spin be accepted and not another? Cheating is cheating.
No matter what sens you have, using it for the sole purpose of incresing the damage you inflict on another player isn't fair, isn't right and is just downright disgraceful.

The game was built for the purpose of everyone having the same chance of winning. Learning the Lightsaber Styles, the Lightsaber types and using your knowledge of them to your advantage in a real time Lightsaber duel against another person.

Cranking up your mouse sens/yaw to inflict much more damage than any given move/swing is intended to do, then calling yourself "skilled" because you can get frags with it is laughable.
The very thought is just ridiculous.

The day everyone can learn from legitamate game mechanics and use their knowledge of the styles and Lightsabers that they have trained to fight with in total fairness and honor will indeed be a glorious one.