>> "The BSD license allows the software to be made non-free."
Let's clarify: Technically, it allows the copy (distributed with the proprietary software) to become non-free, though the original and any other copies of the original are still free. Technically, BSD is more "free" than GPL to the first copier, even if not so to everyone else who obtains it from the first copier. The "subjective interpretation" then is from the point of view of the next guy in line.
> The BSD license allows the software to be made non-free.
No, it doesn't.
It allows non-free software being made incorporating the free software, but the free software remains free. It also allows free software with different terms than the original to be made also incorporating the free software which remains available under the original terms.
Let's clarify: Technically, it allows the copy (distributed with the proprietary software) to become non-free, though the original and any other copies of the original are still free. Technically, BSD is more "free" than GPL to the first copier, even if not so to everyone else who obtains it from the first copier. The "subjective interpretation" then is from the point of view of the next guy in line.