Every professional military or paramilitary (Police, Fire, EMS, CBSA, etc) have some sort of dress and grooming standards. If your supposition is that we need to completely bin those as useless, I'd argue you completely miss the point on why those dress and grooming standards exist in the first place. Even in the paragon of non-conformity CANSOF, I've noticed those folks walking about all have some sort of standard on garrison where it makes sense. If you're suggesting our dress and grooming standards are archaic and need an update, I'm right there with you. There's also an appropriate way to handle dress/deportment issues in a quiet, adult conversation. Flying off the handle is classic loudership, and isn't required unless the individual isn't tracking the nice guy approach.
At the end of the day, people's first impression of you is your dress and deportment. If you can't figure out how to wear your hair or keep your boots clean, then what other details are you lacking in your operational performance?