This is something I think about a lot, too. But recently, I am thinking that ethics can't survive in a non-ethical world - especially in one that doesn't respect ethics.
It's very prevalent, too, not just in engineering. To give a different example: does Adriana Lima stop and think about what Victoria's Secret does to body image issues for girls? That the mass-media promotion of a model's figure gives a too high standard for beauty? No. She takes the money and models. Not only that - but we love her for it. She is insanely popular.
Now in such a world - if given the chance to model, wouldn't you? Even if you are morally against promoting 38000$ clothing items in a world where there are still starving children, even though you think it's absurd that all magazines have skinny female figures on their covers -- if given a chance to make a lot of money by modeling, wouldn't you take it?
By denying yourself the opportunity, you are 1) extremely unlikely to change the system, because you're not so unique that without you things wouldn't work and 2) not even getting appreciated for the ethical choice you made.