You are completely missing the point. UAC doesn't stop malware and viruses from getting on a computer or from starting processes. The purpose of UAC is to alert the user a process is starting and let the user decide it the process is valid or not.
That is why UAC should be set for maximum protection. If UAC set for a lower level of protection (such as the default setting, which is a concession to complaints about UAC), a really clever malware writer could write the code to appear as a program that UAC has been set to ignore.
Seriously? That's like saying one doesn't need auto insurance because they have had or caused an accident. Just because you have never seen it doesn't mean it hasn't happened. And how many people will admit they messed up their machine because the clicked when they shouldn't have?
And we are right back to malware emulating a legitimate program so it can sneak in under the radar. There is a way to do so (there is a tutorial for that somewhere on Seven Forums) but I never bothered to try it; dealing with UAC just isn't that big a deal.
Come on, it takes a whole second or two to read the alert and click on it. Annoying though it is, at worst, it isn't going to cut more than a minute or two out of an entire day's productivity; average users won't see even close to that much.