> "Ideological purity" is irrelevant. The point here is that people are abusing terminology to create ambiguity. As we are talking about software, the term "free" has specific connotations that differ from everyday language.
UE4 is a source-available, gratis game engine. This is fine. It is not open source, nor is it free or libre.
OK, maybe it's better to call it "we're-not-gonna-be-a-dick-about-it" license.