License recommendations are misleading

[rekado]

Unfortunately, the license advice is highly misleading.

If you use an opensource that is under any copyleft license (Example: GNU General Public License), you should understand that your code must be under the same license, meaning, it must be public.

"it must be public" is not true. Copyleft does not mean that your code must be public. The GPL, for example, only says that you must comply with requests for source code if you convey the modified work to users. In the GPL conveying the work does not include network services.

Don't use any code that under copyleft license OR does not have any license associated (copyrighted) in client project.

Why not use copyleft code in a client project? When using any third-party code the licenses must be complied with. It may very well be acceptable for a client to accept, for example, the GPL even if they don't want to respond to requests for source code if they don't convey the modified work to users.

Lastly, "copyrighted" is the wrong term for unlicensed works. Every work is "copyrighted" by default. The correct term is "all right reserved", which describes a work whose copyright holder does not grant a license for any purpose.