Really? You are asking why we should care if a player is performing because he is cheating. Of course we should care.
It is perfectly reasonable to argue that these enhancers should be legal. However, until they are, then how could you not care that some players are gaining an unfair advantage? Don't you care when the opposing team gets away with holding or pass interference?
It's really weird. I'm one of those guys who's a real stickler about cheating. I hate guys who do "anything" to win: the people who try to give hand signals across the table when they're playing cads and stuff like that. If I happen to see someone's cards, I tell them what I saw.
But I feel absolutely nothing about athletes taking drugs to improve their performance. Even though I compete in PL tournaments (in drug-free associations), if someone else is taking drugs... I really don't care. If a football player is taking drugs to improve their performance, I really don't care. I probably should but to be perfectly honest, I don't.
For a long time, you could have taken steroids or some other performance enhancing drug and it would have been perfectly legal and above board. Anabolic Steroids weren't made a Schedule III illegal drug until 1993. There are still "legal" ways to take steroids although if you're an athlete, you will get popped for having them in your system.
If you're wanting to be intellectually consistent about performance enhancement, then you've got to ban painkillers and anti-inflammatories, too. There's nothing more performance enhancing than being able to take a drug that allows you to play when you couldn't otherwise play.
Because of the demonization of steroids and the black market that's been created, you've got a bunch of ignorant athletes in high school and college (and even the pros, probably) who hide that they're doing legal supplements like creatine because they think that they're steroids... and then you've got guys taking things that they shouldn't be taking, things that can kill an injure them without giving them any performance enhancement, because they read somewhere or heard somewhere that such and such compound is some sort of athletic panacea. Not to mention the guys that get stuff black market that may or may not be steroids at all.
A few years ago, lots of bodybuilders started experimenting with taking a type of rat poison because it boosts your metabolism and causes you to burn a ton of fat. The problem is that the dose that you're taking has to be extremely precise. A little too little and it doesn't do anything; a little too much and it kills you. And the thing about athletes and the athletic mind set is that they're fine with running that risk.
So, personally, I think performance enhancing drugs should be legal under doctor's supervision and I believe that the long term effects should be studied. I think that a more open environment would allow us to develop some drugs that could benefit a lot of people and give us better and healthier athletes.
But, that's just me.