If someone has a big accident, and they become horribly disfigured and get corrective plastic surgery, I would argue that that is different from wanting a breast augentation/botox/breast lift/etc. The goal of the former is to return someone to what they looked like before the accident, while the latter is making look different from who they started out as. In this way, I would place body modification into two categories: Corrective body modificaiton (corresponding to the former), and Additional body modification (corresponding to not only the latter, but also piercings/tattoos/etc.). However, all of these things still fall under the broader title of body modification.
The emotional and intellectual part of my brain both agree that Corrective body modification is OK, as well as the tattoo/piercing/etc. side of Additional body modification. However, the two sides still don't quite agree with eachother on the Additional breast augentation/botox/breast lift/etc. body modification.
I know that, intellectually, as someone who is supportive of body modification in general, plastic surgery is not something that should bother me. However, it does. Something like 90% of all plastic surgery is done on women. That is a very uncomfortable statistic. It does not say positive things about the culture of our society. What is so (culturally) wrong with the female form that women feel like they have to enhance it to love/feel good about themselves? And why don't men feel that same impulse towards surgery? When a man gets on in years, he is a silver fox. However, when a women does the same, she just gets old. There is something inherently wrong with this.
I think my emotional/intellectual brain divide boils down to two things:
(1) If our society did not place such a high expectation on women looking young forever, I think that plastic surgery would go down a lot. If women were getting plastic surgery without feeling like they had to do it to be beautiful/love themselves, (disclaimer: not all women are getting them for this reason, but the inequity between men and women that get them implies what I am saying), then I would think of plastic surgery as just another type of body modification, like tattooing or piercing.
(2) Both women and men have the ability to 'age gracefully', so to speak. If a man does not 'age gracefully', he is still given respect and praise. However, if a women doesn't, she is torn down and called names. If we have the ability to 'age gracefully', and yet we choose to hurt our bodies/not take care of them/eat poorly/not manage stress well (not that we always have a choice in these matters, but assuming we do...), it seems like cheating to get plastic surgery to cover up the fact that we didn't take care of our bodies. I don't think this feeling is entirely correct or appropriate, but explains part of why plastic surgery bothers me, as someone who is very active and a large proponent of eating well/exercising/have a healthy lifestyle. I know it is not possible for people to do all of these things to keep their bodies healthy, and that some people don't realize they want to/should until after the damage is too far done. This is something I need to figure out internally.
There are a lot of other topics surrounding surgery junkies, and how the media affects the plastic surgery industry, and this is just one slice of an opinion of a much larger discussion broadly covered in the other posts.