Nikolai Bezroukov has an in-depth paper on the relative merits of BSD style open source license versus the GPL ‘free’ license. Particularly with regard to their economic ramifications. This article appears to be comprehensive, reviewing all the various licenses. ‘…one of the most controversial properties of GPL is the viral property of GPL 2. In essence if you the author of some useful addition to the GPL program that
was widely adopted and developed further you are denied any subsequent modification, enhancement of your ideas in…case you [are a] commercial developer. There are
several consequences of viral property of GPL v.2 (and IMHO this needs to be changed in v.3…’ Thanks to Tim Cook for this link.