You missed his statement about it being embedded into other programs. You see when you embedded a gpl scripting language into a larger program the entire program becomes gpl. This makes it a very bad embeddable program.
IIRC, there is another license (guile, maybe?) that's identical to GPL except it doesn't affect the outer program.
MIT license is far less restrictive.
Of course, but if you want to go with the GPL, you can use exceptions and protect just the part you want.
That's the LGPL, used in the GMP library for example.