There are many motivations such as mindshare, not reinventing the wheel and creating standards that motivate people and companies to contribute to open-source. Ripping-off other’s work - even when legally ok - is not right.
The system is designed to foster collaboration and not to enable shitty business models.
You're describing a thing that happens here, and not even bothering to make an ethical argument against it. People are just supposed to accept the premise, and go on to discuss the implications of it.
> The system is designed to foster collaboration and not to enable shitty business models.
"Spirit of open source" people are arguing that the system wasn't designed at all. You're arguing that open source licenses themselves have little or nothing to do with open source licensing. Instead, it has something vaguely to do with freedom and friendly and collaborative and other nice words. You don't have to be friendly or collaborative to produce either open source or Free Software.
Full disclosure, I'm a shitty open source contributor, but I have some projects on github that I know others have gotten use from, and that makes me happy, not concerned someone is "freeloading".