In general I don't think there's anything wrong with having your own opinion on it.
With a specific girl you're into though... I mean, voice an opinion if she asks what you think of her putting on makeup or leaving her face bare, but otherwise, if she's not soliciting your opinion, it's unnecessary and inadvisable to try to tell her how she should wear it based on what you like.
First, it's kinda true you guys tend to not know the half of it, especially when it comes to what is a "natural" look lol. Besides that though, just like guys don't like to be changed or nagged - same goes with many girls. If she likes wearing makeup, she likes wearing makeup. If you go out with her, I'd do it while knowing and accepting that. Rather than trying to get her to wear less or more or whatever.
I value my SO's opinion so I don't want him to keep quiet. With that said, he met me and I wore makeup the way I liked it. He asked me to be his girlfriend with me wearing it the same way. Fast forward and he asked me to be his wife, again with the same makeup. So it would be extremely weird if after all of that he said he wanted me to changed it. I would be okay if I tried something new and he expressed that he didn't like it. But don't ask me to suddenly stop wearing makeup all together because deep down you want me to change
I don't know why so many girls get offended when guys say they look better without makeup. Or when they say "Well we don't wear makeup for YOU we wear makeup for us." I think I would want anyone, regardless of gender to tell me if my makeup looked bad.
You have the right to say what you like. I guess I can see where it can go wrong because girls may get offended that your preference for example is the natural look while they like to go to a full makeup look with a smokey eye and all. It may seem to some that you're insulting them.
My friends boyfriend told her he liked the natural look and she got angry because she thought he was saying she put too much makeup on.
Either way it gets risky there. I personally don't mind but hey maybe that's cause I don't wear makeup
People don't tell me what to do, I take it into consideration but I am not necessarily obligated to follow it. I don't like makeup at all, and I am going to keep on saying that to prove that there are people who are not interested in a girl more just because she bothers with wearing face paint.