You don't know what the fuck you're talking about.
Sorry, you're the one that doesn't know "what the fuck" you're talking about. Use (including private modification) and redistribution are two completely different things as far as copyright law is concerned. Your insinuation, that using a piece of software or modifying it for private use requires one to accept the GPL, communicates a fundamental misunderstanding of what actions a copyright license covers.
Another important use of OSS is as a learning tool. Seeing how another programmer attacked a related problem can give you powerful insight in how to solve your problem.
Yes, and exactly how does the GPL prevent you from doing that? That is exactly what has been done in FreeBSD development to engineer many hardware drivers - look at the GPL linux driver, and write their own driver from scratch. That is not a copyright violation, nor is it against the spirit of the GPL. If you want to use the code under different terms, you get to do the footwork. Simple as that.