I can see why people like the GPL, but it definitely and intentionally restricts some freedoms (such as the ability to link to non-GPL code, or make proprietary changes) so it can guard others. It's a trade-off not everyone's happy with.
Here's how I look at it: say a company takes some BSD-licensed code, extensively patches it, then releases it under a proprietary license. I haven't lost any rights from this—I can still use the original code without their changes. The difference is the company isn't legally forced to grant me the same rights to their modifications. They're also able to incorporate outside code that can't be legally re-licensed under the GPL—the GPL instead forces them to find or write an alternative.
It's in that sense that the GPL is less free. Its supporters argue that's a good thing; its detractors argue it's a bad thing.
Here's how I look at it: say a company takes some BSD-licensed code, extensively patches it, then releases it under a proprietary license. I haven't lost any rights from this—I can still use the original code without their changes. The difference is the company isn't legally forced to grant me the same rights to their modifications. They're also able to incorporate outside code that can't be legally re-licensed under the GPL—the GPL instead forces them to find or write an alternative.
It's in that sense that the GPL is less free. Its supporters argue that's a good thing; its detractors argue it's a bad thing.