You are absolutely correct. Not everyone "hates" her hair! I should imagine that few do, even more envy the luxurious beauty of it, myself included.
What is an issue is when that hair gets in the way, as indeed it did in Copenhagen. The hairstyle was inappropriate for where she was and what she was doing, to such an extent, that the necessity to move it out of the way detracted from the whole event. It was distracting seeing her continually fiddling with her hair, shoving it out of the way, etc. ad nauseum and, it is not as if this was the first time that this problem has occured.
Take Jennifer Anisten on the Red Carpet. Her hair is beautiful coiffured, bouncing glorious curls. She stolls up the red carpet. Stops and poses for a photo op, moves on, and repeats. That is all she does. However, the Duchess of Cambridge was not doing that sort of thing. When she stopped she was invariably looking down, either at shorter people or children, and as she bends forward, as she did trying to pack a box, her hair falls straight down and gets in the way! And so started the whole hair/hands thing.
When she attended her first evening event in that glorious pink gown, her hair was OK for what she was doing. Walking the red carpet, posing briefly with William for the occasional photo and then in and away from sight. Her hair style was then just a matter of poster's preference and we all have our own opinions.
It all comes down to what works for what she is doing, and that is something she has yet to master. The only real surprise is how very distracting her hair can be, and nobody could have forseen it's potential to irritate. Unkind people are starting to comment that it's a vanity issue because she really loves her hair! Not good a good look and probably neither fair nor correct.