Otto, your comments are right on.
For me it's simple. I thoroughly enjoy developing plugins and themes for WordPress. I do so knowing that my plugins and themes will inherit the GPL, and that somebody can certainly (and they do) take them, modify them, redistribute them, etc. If I were adamantly opposed to that happening, I wouldn't be a WordPress developer. I wouldn't develop open source software at all. The whole reason the GPL exists is to allow people to use, modify, and/or redistribute the software as they wish.
If you don't like the terms of developing open source software, particularly under the GPL, then WordPress development may not be the right area for you. There are many non-open source opportunities out there.
For what shall it profit a man, if he shall gain the whole world, and lose his own soul?