For me, open source has been an incredible way to learn software - it's syntax, it's architecture, it's control flow, it's gotchas.
From my understanding of the license [1], you can see the code, learn from it, do whatever you want with it, modify it if you so please, improve on it, whatever. The only thing you cannot do is sell it. Because you've taken someone else's idea in the first place.
I see this happening all the freakin' time and it pisses me off no end. If I suggest a software to someone, the first thing they as is 'Is it open source?' What they really mean is 'Is it free?' Why? If someone is expecting to get paid for creating software for others, why is the feeling not reciprocated towards the person who's created the software in the first place?
From what I've seen, most managers and software engineers, expect to get paid for their work but all the software which helps them make that money, they expect for free.
I find that attitude extremely hypocritical, honestly.