Except that he is, kinda.
But there is a point to explore, there.
Professor Erkstein's Super-Soldier Serum, and Vita-Rays, are, yes, a super-steroid. They take a weak, asthmatic man and turn him into a beyond Olympic level athlete. With photographic memory and amazing eyesight, to boot. There's really no way to not call them a steroid.
But I also think that it's selling the whole concept, and the character, short to think that way about it. Steve Rogers is not, by any reach of imagination, a "take the easy path" type of person. The comics make that abundantly clear, and I think the film does as well.
We see Steve, weak, frail Steve, work with every fiber of his being to keep up with those around him in boot camp. We see him think laterally, look for options that others may have missed. We see him act, instinctively, for others, not for himself. The film takes pains to show us that a great man, a good man, as Erkstein calls him, lives within a body that betrays him.
For Luke, it's receiving his father's lightsaber. For Steve, it's undergoing a dangerous and painful experimental medical procedure. Honestly, I'd take Obi-Wan handing me a lightsaber over whatever's happening to Steve inside that capsule, screaming in pain, such to make onlookers want to halt the process, then pleading to continue, because "he can do this." The subtext is that what Steve is enduring is not, at all, easy.
Now, that's being a bit facetious on my part, because, yes, there is a direct correlation between the Super-Soldier Serum and steroids. I have a feeling that, if the origin consisted simply with bathing Steve in Vita-Rays, this would never even come up. No one thinks The Hulk, who's great strength comes from exposure to Gamma Rays, has anything to do with steroids (even if you can draw "Roid Rage" comparisons easily). It's the act that Steve Rogers is being injected with a chemical formula that makes the equation.
I think that makes a lot of people uncomfortable. The idea that how you live your life may, in fact, determine your success or failure.
I see it over and over, movie stars, musicians, politicians, anyone in the public eye. There is a faction of our society who, when confronted with a figure, real or fictional, who represents either a commitment or ability to achieve, will automatically feel threatened. The immediate reaction is to TEAR THEM DOWN. Even a cursory scan of the internet will show you that this faction is large, and very, very vocal.
I'm certain that more than a few people reading this are going to start to draw conclusions about me, at this point. I vote Democrat, OK? That said, I also feel like the "everyone has the right to achieve" message (which I firmly believe in), in practice, tends to become "everyone has the right to achieve, as long as they don't get more than I have" (which I most certainly don't). A fair shake doesn't mean everyone wins, it means everyone gets the chance to apply themselves, and see how far they can go.
Which is an interesting place to end up, when you're talking about a pulp superhero character.
Yet, this is what these characters are for. They're folk heroes, mythology, and legend. They're the hero myth, and their job is to help us see the proper way to live and treat each other. To fight that which is unjust and wrong, and protect those weaker than ourselves. It is good for those with power to know they're no better than those without, but it's also good for the powerless to see that valor and courage can be the path to greatness. No, no one may present you with a lightsaber, or give you a magic formula, but you can carry the beliefs and values that would make you worthy of those things into your everyday life.
That's the point. If you want to make it about injecting a scrawny guy with steroids, that's your problem.