I think people get very defensive over this issue - seeing their choice to wear make-up and heels, to beautify and improve themselves as an indicator of shallowness or a superficial interest in frippery, when it's not that at all.
It's just - as is often the way when looking at the world through a feminist lens - looking at the bigger picture and at the impact not on individual women, but on womenkind as a whole.
I think you have to have your head wilfully stuck in the sand not to see that women, en mass, wearing make-up and trying to improve their appearance (in a way that men don't) puts pressure on all other women to look a certain way and to strive for, or measure up, to an ideal which gets harder and harder to reach. I say this as someone who wears make-up and actively likes to look my best, and is part of that viscous circle myself.
Every individual is free to do what they want and make the choices that they need to make - God knows I do - but you just can't deny the knock on effects that decisions made by society as a whole, affect society as a whole.
I know I'm not a shallow person so anyone who says I am is barking up the wrong tree - their problem, not mine and I wouldn't take offence as I know it's not true. But I'm not going to deny that buying into the make-up and beautifying thing myself impacts more than just myself and perpetuates pressure on other women and especially young girls.
I don't really get why people refuse to acknowledge that, beyond seeing it as a criticism of their own choices as I say at the beginning of my post. But, yanno, why take the criticism? Have faith if your own choices and the reasons for them. :)