I think this is a fascinating question. I've seen people who suffer from ADHD or other such disorders who say that it is "unfair" when other people use drugs like Adderall to help them focus more to cram for a test, a mental equivalent of steroid abuse, I'd imagine. But popping adderall before a test doesn't make you do well on the test - it allows you to focus and prepare more for the test, and get the most out of your knowledge and ability. I honestly don't fully know, because the media tends to obfuscate this but, what do steroids do, precisely? Do they actually build muscle? Or do they enhance the growth of muscles when training? I imagine someone taking steroids and then sitting on the couch gets the same impact as someone taking adderall and watching TV.
So what these drugs do, then, are that they enhance some quality that you already have - if you're studying, you study harder; if you train, you train harder. I think we can also ask a similar question: If you're drunk, or if you're stoned, are you still you? Are your actions while under the influence just you with less inhibition, or judgement? Legally we think so - you're treated as accountable for harm that befalls you or others (see: drunk driving). I don't think that this is a "truer" self because I consider inhibition and judgement to be just as much a part of a person as the things those qualities hold back. But it is a self.
We change all the time - You now is not the same you as the five-year-old you. And I don't mean that in a metaphorical way, none, or almost none of the cells in your body are the same cells you had when that body was only 5. They're always changing, and replacing themselves. Meanwhile, your mind is always changing, updating, making new connections and losing old ones. But we've decided that all these different people - you at 5, you at 13, you at 21 and 35 and 80 - are all the same person, many minds and bodies threaded over a single string of life. So knowing this, why would we decide that someone is a "different" person if they are under the effects of any drug, be it a steroid, an anti-depressant, or a joint?
It's understandable why steroids are largely banned - they definitely do make it harder, maybe implausibe, to compete with someone who is using them for those who don't. That said, if there were a steroid-like enhancement drug, with no side effects and a definite improvement in everyone who took them... why ban them? Why not treat them like a fact of life? Perhaps they could be abused, but so can any drug, including plenty of over-the-counter medications. It still requires dedication and physical prowess to make good on any enhancement drug, it just helps to achieve new heights. And besides that, consider that some people maybe just have a genetic predisposition towards athleticism! Is it unfair that a 5'10" guy in the NBA is at a disadvantage against 6'6" players? Maybe, but no one will propose cutting off some of the tall guys' shins. If we allow for natural advantages, why not say that we'll make an allowance for unnatural ones as well?
If we had the exact same thing for research scientists, a drug that had no side effects and helped them hyperfocus on their work and freed up neural pathways for enhanced intelligence... why on earth would we not use it? With an army of men and women with mind-enhancing drugs, we could discover the cure for cancer, or learn how to achieve efficient interplanetary travel with humans. If we can build a better human, why wouldn't we?