Like Koppenberg said, it is in part the fans who suck.
That's why I start threads on people I believe to have been clean, even though they aren't necessarily champions--like Collins, Patton, Lemaitre, etc.
I really do appreciate performances I think were clean, and laugh at those I think were doped, because I know they are more absurd than impressive.
Also, one other thing: even among highly-trained athletes, at least in the sprints, juicing can make a much greater difference than the 2% suggested. Take Jeter as an example--from 2004-2006 she was running mid-11's, and she got down to around 10.7, which represents a 0.80 improvement, which is 7% of 11.5
That is huge. Juicing is done by not only those who have worked hard and might be within 2% of the top, it is also done by those who can see the top, but who are nowhere near it--like an 11.5 female 100m sprinter.
Also, masters athletes juice. Why? Overcompensation and unfinished business. Check it out: I've gone 11.8 this year, not all-out because of injury. I could easily have gone 11.5, again. What if I started using? Given how hard I train, a decent response could be expected. Let's say my response wasn't as dramatic as Jeter's--let's say that I would get to 10.8 That would be very, very close to the masters WR in my age group. If I responded as well as Jeter, I would have it.
I'm sure that some people find this kind of incentive compelling. Personally, I don't. I'm so not-serious about it that I won't even run a meet that takes more than 15 minutes to get to--but some masters take it very seriously, maybe trying to recapture youth, or win some races against local competition, something they couldn't, or didn't, do when competing open, or in college, where the times are faster than at local track meets.
There's also just the effect of aging that people are trying to overcome. With masters, the reasoning is obvious--but I think it applies to open athletes as well. After a guy hits 30 or 35, performance slips, no matter who you are. Check out Lagat at the Olympics, you can tell that he is a step slower at 37. Now, nobody would deny that Lagat is still elite--of course he is--but when people in his position decide to juice, it's not necessarily to get that 2%, it is to regain something that has just recently been lost. And, it can happen even at age 30. People would take stuff not necessarily to win, but to get back to feeling that winning is an actual possibility, and to reverse the inevitable trend of getting slower and weaker. To feel better about themselves, in short.
Anyway, I think that the benefit even among the highly trained can be very much greater than a mere 2%, and that the benefit among the less-highly-trained can be absolutely gigantic. If it would be 7% in people like Jeter, I would say that 25% or more gain would be achievable for a weekend warrior.