Generally, I am not in favor of implants. They don't look or feel real. I would prefer a woman with reals B cups to one with fake dbl D's.
If it's for cosmetic reasons like after a mastectomy or double mastectomy, then I'm perfectly fine with it. That's a life changing and traumatic surgery. Implants in this case have a necessary physical and psychological benefit for the patient.
If a girls not happy as she is then fair enough, its her body so she can do what she likes with it. Personally thou I don't think its natural, there's just something about implants that makes a girl seem fake.
I don't care for it. They usualy don't look or feel natural, but if a girl really really wants them that bad then its up to her.