What's Wrong with Linux?
Linux (being the Linux kernel, not a Linux distribution) is almost entirely free software, licensed under the GPL v2. This allows users to observe, change, and distribute the kernel however they see fit. However, by default, the Linux kernel includes proprietary binary "blobs" that allow specific drivers to function. Having proprietary software on your system means that you have no control over it's functions and no way of even knowing what it's doing.