It´s not only about good/bad looking helmets or hiding nice faces.
Some helmets may look good, but are not suitable to certain armors.
Like full plate helm and robe or leather armor.

There are three simple facts:

1) The absolute majority of people prefer to be able to "Hide helm".
2) Doing this is very easy for developers, it takes an absolute minimum of time.
3) IT IS ONLY SELECTABLE OPTION! NO ONE IS FORCING YOU TO USE IT!

Anyone who reads this and still feel need to share with us his indisputable opinion how "bad idead" is be able hide ours helms is simply troll.