Now I can no longer recommend the MPL to people that don't want to license as GPL and don't want their code to suddenly become GPL'ed because someone used it in their project.
The license requires that Modifications (as defined in Section 1.10 of the license) must be licensed under the MPL and made available to anyone to whom you distribute the Source Code. However, new files containing no MPL-licensed code are not Modifications, and therefore do not need to be distributed under the terms of the MPL, even if you create a Larger Work (as defined in Section 1.7) by using, compiling, or distributing the non-MPL files together with MPL-licensed files.
Yeah, if you want to avoid any copy of your code becoming GPLed, avoid GPL compatible licenses. But if you're releasing your code under a free license, I'm not sure why you would specifically not want GPLed copies floating around too.
Generally speaking, if the software is free and not subject to copyleft or a choice-of-law provision, there is probably nothing to stop users from redistributing it under the GPL.
This seems to say that you can block that possibility:
"Software can become “Incompatible With Secondary Licenses” ...the original author marks it as such by adding the file header in Exhibit B"
BSD, MIT and other permissive licenses also have this "problem" that they can be used as GPL.