Having a physical preference in the opposite sex when it comes to dating and relationships is, literally, shallow - since it's something that you can see right off the bat.
But not having that dictate your choice overall - makes you, your behavior and your choice of an SO, in its entirety, not shallow.
Simple as that.
Yes, preferences are sometimes looked down upon - mostly because they tend to exclude people based on superficial traits they may or may not possess.
BUT > the smart person always knows that you shouldn't exclude anyone because they aren't tall enough or skinny enough or booby enough...
Yeah, sure it's nice to fell those traits in someone, but on an emotional level, you don't really, truly need them. You just simply want them.
Needs > Wants