Don't set theme if user has set a theme in profile

Users can select their personal theme if they have permission to do so. The question arises : if a user selects a theme different from the site default, should this context override it? I think not, because if a user-specific theme takes precedence over the context-supplied one, a user or administrator can easily disable the user-define custom theme setting. However, if the context takes precedence, then there is nothing the user can do about it.