[fctorial]

If open source weren't a thing, software development would be much bigger pain than it is now. If something goes wrong in the code you're using, you can look into the source and at the very least implement a hack if you can't change the base. All that goes out the window with open source if you throw it away.

Also, software developers would be much more rare since the cost of learning would've been much higher.

[unilynx]

That doesn’t require open source, just the source. (Some?) Borland compilers used to come with the source of their standard library, which allowed us to hack around bugs in their time() implementation, but it wasn’t open source.