Well, it's a fine balance. Adrenaline does help you focus (a reason why people with ADD are often adrenaline junkies; also the reason why my ex would procrastinate on projects like writing papers - the stress of the pressure of being up against a deadline actually focused him).
On the other hand, if you're feeling the physical effects of excess adrenaline, they can cause sweaty palms, racing herat, tremor.
When it comes to stage performers, I find they only usually need to use it a few times before they overcome their fear. But I hear what you're saying about competition and doing it clean, and I respect that.
Since beta blockers are a common blood pressure medicine and heart medicine it seems like they would be hard to ban, but I don't know.
