Something in my lawyer's mind says me that a module not explicitly under GPL, cannot become GPLed because it uses or otherwise links (statically or dynamically) to another GPLed module.
True. The collective program may have the GPL apply because it is a derivative work of a GPLd component. That does not mean that all of the other components must have the GPL apply to them.
Suppose the license on some module "A" requires that all other programs, modules, libraries, ... must be under a similar license if they make use of module "A".
Use is irrelevant. The GPL only applies to distribution.