No offense, VERY good question.
I like your thinking, because it always starts with a premise.
It's true our bodies are temples (for the Holy Spirit).
- Jhn 2:21 But he spake of the temple of his body.
- 1Cr 6:19 What? know ye not that your body is the temple of the Holy Ghost [which is] in you, which ye have of God, and ye are not your own?
Once again you're beginning with the presupposition that steroids are harmful, when if applied and administered properly they really aren't. Thus, if I'm SAFELY taking them to enhance my general well-being (physical, mental, etc.), and not abusing them by the actual definition (causing harm to myself or others) how can they be wrong?
You mentioned stealing and murder which do harm others, and marijuana (throw in alcohol, rec drugs, etc.) all of which cause potentially dangerous altered states or unnecessarily damage the body or it's cells. Steroids are medications designed to make one better, I simply manipulate them and the raw materials (nutrients) to make myself better.