I don't think that's really a given: The product of our past evolution doesn't necessarily represent our current needs and interests. More muscle mass is costly to maintain, which could have been unwanted in food scarce environments; living long lives might be evolutionary irrelevant past reproduction age...
Think about teeth for an obvious example: The body is able to grow them, and some animals do it constantly - yet losing our adult teeth (due to aging, accidents or whatever else) does not cause us to grow new ones. It would be hard to dispute that growing a replacement tooth would be beneficial to a person in our current context and lifestyle, but evolution has not reached that conclusion.
Edit: Replying also to your second phrase (the message I'd be giving to my potential children) - I don't really see why, if current research points to minimal to no dangers for short term use (about as harmful as light alcohol consumption), I should be treating it as such a big deal. If anything, I think it would be a positive lesson that they should make adult choices for themselves by taking appropriate steps to be informed about the pros and cons of it.
Ok, fair points. But then again, by going the steroid route you and your kids would be excluded from participating in any sports matches (except perhaps bodybuilding contests). How would you feel about that, and about how others would view you in this regard?
If steroids would be a net positive for the body in general, then evolution would just follow the gradient and produce more of it.
> if steroids are indeed a net positive for the body they might even have legal choices available by the time they're adults
That's a huge "if ... might" there. Again, what are you telling your children? That gambling with your health is ok?