GPL uses copyright and its viral aspects strongly to try to undermine copyright's goals. That's precisely why it is viral, because it is copyright, and doesn't make it any less viral. BSD-style licenses' terms minimize the viral impact of copyright on the free use of the covered work rather than trying to maximize that viral tendency toward achieving some opposing goal. The distinction still works fine. GPL is viral, as contrasted with BSD licenses, but not as contrasted with proprietary copyright, and for the same reasons.