I think Dietmar makes sensible points. Both views are right, in a way.
I mean yes, if people release source code and upload it to Aminet, they're probably going to be okay with you modifying it and also uploading to Aminet. Also, as long as you are distributing the modified source code too, and do not place additional restrictions upon your release, then yes, it's probably true this is compatible with most open source projects (in fact, I believe it may be true by definition for Open Source - Dietmar is right in that there is a distinction between Open Source, and projects that might have the source available to view).
But I suspect disagreement arose because of the implication that you can do what you like with the code. As stated, licences like the GPL place restrictions on code. I'm also not sure if koaftder's point was that certain restrictions were bad, or just that it's simpler if developers use standard well known licences?
If you place something in public you still own it, but what is done with it is out of your control.
This simply isn't true, legally. Just because you release something in public does not mean people can distribute it as they like - be default, any further distribution is copyright infringement. This goes for anything - come on, we aren't still perpetuating the old myth that if you find it on a webpage, it must be free to distribute?
This might be your opinion, but it is not what the law says.