A not uncommon reaction, in the wake of the Armstrong USADA revelations is to say “well, why not make doping legal? Then at least it’d be fair.”. There’s a number of arguments against this, from vague ones about sporting fairness. However, the most compelling argument, to me, is about protecting the health of athletes.
First though, it’s important to note that those who want doping to be legal can go set up their own “Doped-Cycling Federation” and setup races. There’s nothing stopping them, at least in countries like the UK and USA. E.g. Lance Armstrong can still compete in bike races and tri-athlons that don’t sign up to anti-doping, and which don’t care about the USADA ban, and he has in fact done so. Arguing that doping should be legalised therefore is a redundant argument, because it is already the case, and there are competitions for people who think this way. Body-building has doping tolerant (and intolerant) factions apparently; baseball in the US seems to tolerate doping; there are cycling races without doping controls; etc. etc. Dopers are more or less perfectly free to to dope away in those competitions!
However, many other athletes would prefer not to dope. It can have serious health risks. Both high-consequence risks, such as death (blood thickening from too much EPO; bad blood transfusions; aggressive, accelerated cancers from abusing hormones such as EPO, testosterone, etc), as well as more insidious and higher-probability health problems that can arise from continuous abuse of steroids and hormones, such as calcium-depletion in bones leading to premature osteoporosis, suppressed adrenal and immune system function leading to a wide variety of possible problems (e.g. otherwise fit people being completely floored for months by normally harmless viruses that we nearly all carry without much harm; auto-immune disorders; degeneration of connective tissue; etc).
The list goes on and on, it’s literally as long as the side-effects lists in the advice sheets that come with the substances being abused.
Many people, in and around sport, feel that we shouldn’t be forcing our young sports-people into having to dope in order to pursue their dreams and make use of their talent. They feel athletes should have the option to compete clean. That means you need to provide sports with incentives and measures to discourage unhealthy, unnecessary, risky medical intervention – so that those who want to compete clean have a venue where they can have a decent chance. This is why many sports bodies, including ALL that are affiliated with the IOC (directly or indirectly), are signed up to the WADA Code.
Maybe those measures are imperfect. Maybe they need to be improved. Maybe more needs to be done (e.g. there are credible allegations that some major sports like football and tennis are ignoring their own PED doping problems). However, protecting the health of athletes is a compelling reason as to why we should try to provide doping-free sporting venues, to give them a credible way to compete without having to use risky medical procedures and products.