Not a native speaker, so I hope this makes sense. In my opinion, of course you can. Just like you can look good wearing a hat or another type of a scarf etc. Not being able to see somebody's hair doesn't make them ugly, although if you have beautiful hair it can add to your beauty. Whether you wear a hijab or not does not change your facial features, so my guess it that not finding a person wearing a hijab attractive would be due to the fact that the person simply isn't attractive (subjectively), or because of the impression you get (a religious person, a muslim) if your opposed to these ideas. So basically, it doesn't have to be about the fact that a person wearing a hijab is not attractive (unless they are), but the fact that it portrays a message that some people find unattractive.