I always aim for the best I can do, and in the case of my degree that was a 1st. If your best is a 2.1, it's good to realise that early and maintain that standard, but if a 1st is achievable there's absolutely no reason why you shouldn't aim for it.
I do partly agree with your statement that a 1st with no extracurricular activity or work experience will probably not be as impressive as a 2.1 with lots of experience for certain companies. However, it's perfectly possible to get a 1st and get the relevant experience. If you can do both then again, why not aim for a 1st?