The fact that it runs in kernel space(being a driver) makes it a risk. Applications are supposed to be ran in user space, which means that the OS does various kinds of management for them, like memory protection. This means that a regular application can never do something 'wrong', like overwrite memory of another application, access files the user doesn't have permission to, or make the whole operating system crash. When you run applications like this that use their own drivers to gain kernel space access to your system, its like stepping back 13 years into times of Windows 3.11. Yeah, there are some applications that require this kind of access, I have a packet sniffer and a registry monitor application installed on my system that use similar drivers to do their thing. But a game doesn't need such access, the only reason why starforce runs in kernel space is because it makes debugging it, and thus "cracking" it, harder. This is certainly not a good practice, and the fact that there apparently are vulnerabilities in the driver that can allow any thread to gain administrator priviliges is another bad thing. And there are other concerns too, like future support as I mentioned in my earlier post.
But starforce is not the "end of the world", its just something I prefer not to have on my system. If a game requires it, I have no choice but to not play the game. And I'm certainly not going to buy games that I cant play. If it becomes a common practice to use drivers like this in games and applications, we'll soon be in a situation where every application we run throw all protection out of the window and just run in kernel space. Then we might as well go back to using DOS & Windows 3.11 and say goodbye to all progress that even Windows has finally had to actually making it stable.