Well, to me anyway, wrong reasons would be:
1. To look good for women.
Basically any amount of muscle mass will look good to a girl as long as you're cut.
I've seen girls think guys with 14" arms are huge, simply because these guys are pretty cut.
And I have a buddy who actually shrunk down to 16" because at 17" most girls would tell him he was too big? WTF??
Why do you need to waste $$$ and time to juice if all you want is to get layed? I agree with an Article in T-Mag where it says that basically the only reason built guys get layed more often is because their looks give them more confidence. I think in most cases that's true. Of course if a girl works out, then it's a totally different story.
2. To be the biggest guy in the block.
I wouldn't really consider this to be that bad, but it's not necessary. It's a false sense of power. Seriously, when a little skinny dork can pull out a TEC-9 on you, what difference does it make if you're 350lbs?
I was one of those nerds in school who got picked on constantly, so I took up bodybuilding as a way of intimidating my enemies. It worked to a certain extent, but there's a limit where size is not useful anyone.
I rather have 16" arms and know how to fight than 20" arms and get my ass whopped open.
Right now my arms are 17", but I'm not cut, BF about 20% which I have to lower.
My goal is 18" arms, but you're trading off fighting ability with this. I've done some Judo, and I've seen how easy it is to grab big guys and toss them down. It's pointless to want to get huge.
Please don't take any of this personal, as I am just talking in general, and not really at anyone specific.
The honest truth is, if using AAS helps you with your goal in life, then you're doing the right thing for you...