Columns which are “Hidden” in standard views appear by default in the Row Detail. Even if the choice is made to hide the columns in the row detail, the default goes back again to showing all columns when viewing Row Detail next time.
There are two related issues:
(1) Appearance/Usability - it would be helpful in any given view to default to certain columns remaining hidden so as to not clutter the workspace
(2) Security/Privacy - Though at first glance it appears that View-Only readers cannot see hidden colums because there is no option to turn the columns back on in the standard view, in fact all they need to do is to go to the Row Detail, where all hidden columns are visible by default.