The only problem of the GPL (and I'm talking about GPL2) is that it is ambiguous. You don't know the extent of what's allowed depending on the author.
By more free I meant the balance between the producer and consumer, maximum freedom to both parties without conflict. You want to make sure the actual code stays free, which GPL does and BSD doesn't. You want to make sure the consumer has maximum rights, which BSD does and the GPL doesn't. The MPL balances this perfectly IMHO: the code itself and modifications to the code itself remain free, and consumers get maximum rights just short of violating the freedom of the code. Depending on the author, the GPL may mean that more than just the original code and modifications must be made free, such as software that only links to the original code.
It's not that the GPL2 is bad, I just don't like the ambiguity that can lead to overreaching. And I hate overreaching in licenses.
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The GPL is the GPL. Either your code is under the GPL or it isn't. The requirements are spelled out in the license.
The MPL balances this perfectly IMHO: the code itself and modifications to the code itself remain free, and consumers get maximum rights just short of violating the freedom of the code.
That's kinda like balancing between the right to keep and bear arms and sensible gun control. You can't have one and still have the other.
If you want your code to remain available then letting the end user decide what to publish and what not to is not a balance.
If you want the maximum penetration of your software then putting any restrictions on what the end user can do can prevent that.
There are different reasons that people use Open Source licenses. That's why there are different licenses.
Pick the license that fits your philosophy and use it. Respect the right of other users to use a license that fit's their philosophy.
The MPL fits a different group than either BSD or GPL. And that flexibility, that ability to pick a license and have it do what you want is what matters.
The BSD license gives maximum freedom to the user at the expense of the freedom of the code. The GPL gives maximum freedom to the code at the expense of putting restrictions on the user. The MPL takes a little freedom from both sides.
So, depending on how much you care about where you want the freedom to be, different licenses are more suitable for that purpose.
The license you pick may be "better" for your purposes. That doesn't make it "better."