[bruce511]

The primary difference between GPL and OSS (BSD, MIT et al) is one of philosophy.

The FSF believes that closed-source software should not exist at all. Their license is explicitly designed to make it completely incompatible with closed source software. Updates to the license (GPLv3, AGPL etc) are specifically designed to close loopholes which closed-source companies were exploiting.

OSS by contrast sees Open Source as a public good, but lives in a world that tolerates closed-source entities. It's possible to use an MIT licensed gzip library in a closed-source program, with GPL you cannot.

OSS says "Open Source us better, but closed Source is better than nothing." The FSF says "it should be Free, or you should not use it at all."

Both OSS and Free licenses mandate that users should be able to build binaries from Source. If I make a change to the gzip library then my users are entitled to those changes. (There's no "giving back", only giving forward.)