Not to be a jerk, but it's about what _you_ value. If you value money (or lifestyle, or whatever drew you to advertising) over whatever you were doing previously, you've had your way. If you don't, you have the choice to go back.
Don't feel bad about not working in the right industry; just remember that there are thousands of ways to help progress the state of the art, raise money or awareness for those progressing the state of the art, or even just helping people and their families dealing with cancers.
I don't work in a philanthropic job. I would like to, but value the financial stability of something further removed from pure altruism.