[Tomte]

> I can create a fork of any MIT licensed project right now, and relicense it as GPL

A common misunderstanding, but no!

You can incorporate the MIT project into your X-licensed project, and now have three parts you need to consider: the MIT project, your X project and your (presumably x-licensed) composition of the other two projects.

It means, for example, that when distributing your composite project, downstream users do not only have to comply with X, but also with MIT (for that part). So they havbe to reproduce the MIT license (they would not need to do so if you truly relicensed the code!), and they need to distribute the copyright marks of the MIT project etc.

[jimjag]

The entire work can be licensed under GPL, but those parts that were MIT remain, individually, still under MIT. MIT specifically and explicitly allows for 'sublicense'ing

[Tomte]

Correct. And the combined work needs to carry the MIT license text and copyright attributions for the MIT software authors. With binary distribution it must also be overt, not hidden in some source code drop, but directly accompanying the binary.

Many people who talk about relicensing never credit the MIT developers or distribute the MIT license text. "Because it's GPL now."

I don't think that you believe that, but many developers do.

Some don't see the need for source code scans for Open Source compliance, because the license.txt says GPL, so it's GPL. Prime example is the Linux kernel. There is code under different licenses in there, but people don't even read https://github.com/torvalds/linux/blob/master/COPYING till the end ("In addition, other licenses may also apply.") and conclude it's simply GPL 2 and nothing else.

Also be aware that sublicensing is not the same as relicensing.