Some swing applications sets the look and feel to some specific value without providing means for the user to change it. This forces the application programmers choice of look and feel on the user, forcing for example a windows user to use a Motif GUI, or a site that wants to have a consistent Motif look and feel might be forced to use the Metal look and feel because the application programmer happened to prefer it.

The user should have some means to override the applciations choice of look and feel.