Damn you guys use weasel words.
You have to think precisely about these issues, or you will easily fall under the influence of any "weasel" that comes along. I encourage you to read up and test what I am saying yourself.
But only is true if your code never touched my code. The second your GPL code touches my codebase, if I want to redistribute the codebase, I *must* do so under the GPL.
This is a very backhanded way of putting this, considering that you are the one deriving your code from my GPL'ed code in this example. Yes, if you really are deriving from someone's code (as opposed to mere aggregation), then yes, you must obey its license. (Probably a lot of commercial licenses don't even allow "mere aggregation", but the GPL does, as far as I know.)
Remember you are fighting a war of ideas, and not everybody agrees with your ideas.
I'm not sure I'm much of a soldier in the war. Rather, if I spend my weekends writing code for the public good, why shouldn't I license it as I see fit? Sometimes I use Open Source licenses and sometimes the GPL. Even the FSF uses non-GPL licenses when they perceive the need.