For pro riders the reasons to juice are pretty obvious. Money, pressure and fame (to name a few).
For non-pros it also seems there are a lot of reasons for riders to juice (based on the rate of positives) but what I'd like to explore is the fundamental difference between Europe and the rest of the world as it relates to motivations for doping for these riders.
In most of the world, cycling is an elitist, white collar sport (as a generalization) that appeals to those who can afford it. Even after you are fully equipped, there are still considerable expenses that keep the sport focused on those who have enough disposable income to participate.
In Europe, it is a blue collar sport. For those who can't afford it there are clubs and institutions in place that help offset the cost of the equipment. Also, older riders are more likely to mentor younger riders and this means handing down perfectly good equipment. In Europe, traveling to races isn't nearly as difficult as you can usually find something close thereby greatly reducing financial burden number 2: traveling expenses.
These are fundamental economic differences that create very different motivational factors.
My point is this:
If you were an aspiring racer in Europe, and someone told you you could quit your job at the tire factory and make enough money to support yourself and your family by using this potion, I can understand the temptation. You don't need to be good enough to ride on a Pro Tour team, just good enough to get a Continental Pro contract.
The problem is, even if these riders are aware of the dangers, poverty is a great motivator. What you end up with is a string of kids who have nothing to loose but everything to gain, being fed into the machine until a champion is spit out the other side. How many other riders were simply chewed up by the doping machine and discarded?
To put in in context for those in NA, cross the pond. Now you are in an impoverished urban center in NA. Go down to a local BB court, open up your little black bag, and tell some kids that if they juice, they could make it big. It may kill them, but it may not. How many would jump at the chance? This may be the only time opportunity ever visits their door.
I'm not advocating doping so please skip that bit in your replies. I'm trying to understand what gets people, who are not already pros, to this place.
Another point I'd like to make is that dopers come and go but the machine keeps running. Catching guys and handing them suspensions does nothing to dismantle the mechanisms that support doping in the first place. For ever rider caught, how many more are being stuffed into the machine at the other end? Some will win, some will lose and some will die. And who is it that really benefits from this machine? What is the motivation for those who keep the machine churning?