(Of course, you could equally spin it that these are bad things - an exercise for the reader.)
The FSF takes a pretty major logical leap by considering dynamically linking a work to a GPL library to be creating a work that falls under the GPL.
Both EU and US scholars doubt that mere dynamic linking constitutes making a derivative work. (Specifically for the US, Galoob v. Nintendo ruled that a derivative work "must incorporate a portion of the copyrighted work in some form"; which obviously isn't the case with dynamic linking. - Legal scholars in the EU have come to similar conclusions when it comes to the various EU copyright directives.)
Generally speaking it's untested enough ground to kinda avoid the GPL for this usecase anyway, but the FSF's Legal FAQ presents things as fact in a way mostly only benefitting their cause.
A key question is if different aspect of a work should be considered separate independent works communicating with each other or as a single copyrighted work. In games people often talk about DLL files (in terms of modding), game content like images, video and sound, game engines, game and sever code. How much and what aspects can be modified without the permission of the copyright author?
There are generally three arguments I have heard in favor of a "single work". One is that everything will eventually be copied into memory, and thus while independently they may have individual copyrights the combined work which the author calls "The Game" is a single work.
The second argument is that all this technical details doesn't matter for a judge or jury. What matter is what those people perceive as a single work. Technical aspects like did the copying arrive there through the internet, a CD, a DLL file, or what have you isn't that important in determining the question about a single work vs interoperability between different independent works. It is all about the experience for the end-user.
The third argument I hear is that DDL files or programs that dependent on them are not independent. One can not run them independently, they are generally not developed independently, nor can the "single work" even start if parts are missing. Putting files into DDL is just a form of splitting the work into multiple files for technical convenient reasons, which is not a basis to form a legal distinction between a single work and multiple independent works. If the technical aspect would allow this then anything sent over the internet would loose copyright, since content is split into thousands IP packages which individually might not be large enough to be copyrighted.
But since GPL and LGPL are compatible licenses, can't the non-free author just fork the GPL to an LGPL version and then use it? A bit of inconvenience and technicality involved but still a workable workaround.
In an extremely simplified version, LGPL says you can only use the software if you guarantee A and B, while GPL says you can only use the software if you guarantee A, B, and C. Since {A,B} is a subset of {A,B,C}, licensing the LGPL software under something that requires A, B, and C guarantees A and B and so is fine by the LGPL. However, since the LGPL doesn't require you to guarantee C, then licensing software under the LGPL will not maintain all the requirements you must maintain to use GPL software.
You can static link code under the equivalent version of GPL license. The point of the LGPL was to compromise so non-free software could still use free libraries. I was unaware of the static compilation aspect of MPL - that's interesting.
Those that want to take the work of others for free, get the same payment that they are willing to pay upstream developers for.
Otherwise they can dynamically link it and take it as it is, or if it doesn't suit them, pay for the commercial license instead, and share their gold coins with upstream.
EDIT: missing words
