Donkey, don't generalise. I agree w/ you on personal issues. However there are many bros, and on this board also, who do it purely to brake through platue and increase gains. If you look at it only from insecurity point of view, then all who train (natural or not) have insecurity, because why do they start shaping up their body in the first place? Don't like how it looks? Insecurity?
I started lifting in my teens. I admit that at first it was becuse of teenage insecurities and wanting to be mascular and strong for the sake of peer opinion. However, 15 years down the line, I simply love to train and be hard. Kinda developed into a habbit now, whereby I actually enjoy the process more than the result.