"Why can't they just build muscle the proper way?" Lol, what can take a natural bodybuilder 2 years can be done in 6months if you're taking steroids. You ask is there a safe way, well there are light orals which are not too hard on the liver but you would not get anywhere the gains had you've used a more potent/toxic oral. there are many potential problems and side effects baldness, high bp, liver damage, testosterone shutdown, rage, b*tch t*ts,enlarged prostate etc. But there are many supports that bodybuilders take to keep these away.
Ankou they do not return to normal when you stop taking steroids as your testosterone production has ceased and you need to take various chemicals at the end of a cycle a time known as "Pct" (Post cycle therapy) to restart your htpa (hypothalamic-pituitary-testicular axis) and even then some guys stay shutdown.