Plastic Surgery
Cosmetic Surgery (often referred to as Plastic Surgery) generally refers to elective surgery (rather than required surgery) done by a doctor in order to make a person more physically attractive. This includes procedures such as liposuction, penile lengthening, and breast implants, but does not generally include atypical procedures such as subincisions or implants in the sense of 3D-art.
Limitations of Cosmetic Surgery
In most Western nations, cosmetic surgeons are restricted (by medical association politics and sometimes law) from doing procedures which move people away from the culturally accepted norm. Even introducing a new procedure can be difficult, and doing a procedure like the ones you might see in BME/extreme can put a doctor at risk.
That said, cosmetic surgeons are often able to assist on reversal of procedures such as transdermal implants, meatotomies, stretched lobe "correction" and so on, and because of their experience with fine suturing and scar reducing techniques can produce very nice results. It can also be for those who are suffering from a change of ideals.
Common Criticism of Cosmetic Surgery by "the Modified"
Many modified people feel that typical plastic surgery procedures like breast implants are "wrong" because rather than embracing an individual aesthetic, it embraces (perhaps by coercion by television and the media) a "group" aesthetic. Thus the act of getting cosmetic surgery is sometimes seen as a submission of the individual to the group, and a move away from individualism.
Primary Counter-Argument to Criticism
The aesthetic ideal that is the cultural norm is that because it is what most people agree that it is what is attractive. Thus it is also their individual aesthetic, even though it is shared by the group — so other than being more common, the motivation is often the same as with atypical modifications (to make a person more physically "in alignment" with what they internally consider their ideal self). Reputable cosmetic surgeons are bound by law to screen their customers to ensure that they want the modification for themselves and are of sound mind, which minimizes the chances of people being forced by cultural pressures.