You're not taking anything away when building open source software into proprietary systems, other users are free to get the original project just like you were. FSF licenses just restrict the way I can release my derivative work.
At best the FSF license can be seen as an understandable restriction on freedom to preserve open source software by requiring reciprocation. To me there is no question that MIT and BSD licenses are more free. FSF style licenses made more sense when open source seemed like it might be a delicate beast at the mercy of proprietary forces, I think its clear now just how robust open source software is.
> You're not taking anything away when building open source software into proprietary systems,
I don't think that's necessarily true. Imagine an open source system that's fairly popular, but with just a few developers. ProprietaryCo hires them all up, and users realize that if they want improved versions of said project, they're going to have to pay, or find some new developers. Far fetched? Not really, it's pretty similar to what Sun Microsystems did.
So, there is some risk to the community. What 'protects' BSD licensed projects best is to have a strong, and diverse development community, which is one of the things that the Apache Software Foundation tries to encourage.
I guess I imagine that style of thing will be a rarity. Its not specifically proprietary software thats creating a problem in that case though, its that a company is stopping development on the open source project by hiring all the programmers away, that could happen with a FSF license as well.
With a GPL license, you could hire up all the developers, but unless you really got all of them, or had a copyright assignment, it would be very difficult to take future versions proprietary.
As to how often that kind of thing happens, it's hard to say. BSD/Sun is a big, obvious case. It would be interesting to get statistics on others.
My general strategy is to use BSD style licensing when my code might be included in someone else's project (Hecl), and GPL if it's a "finished product" kind of thing.
You're not taking anything away when building open source software into proprietary systems
From Stallamn's view, I'm pretty sure you're not taking anything away by restricting the creation of more proprietary software. Proprietary software pretty much doesn't exist for him.
To understand his point, you really have to apply all of the moral frames relating to 'freedom' to software licensing. In that view, to license software without distributing source is akin to licensing software with a clause to give up your first born.
At best the FSF license can be seen as an understandable restriction on freedom to preserve open source software by requiring reciprocation. To me there is no question that MIT and BSD licenses are more free. FSF style licenses made more sense when open source seemed like it might be a delicate beast at the mercy of proprietary forces, I think its clear now just how robust open source software is.