Many reasons, but for me the main two are:
1. you want your freedom respected, but you don't want to respect the other person freedom. 2. GNU exists because RMS didn't pirate UNIX, he created something new with a new license, GNU. That is, in my opinion, the principle what should empower a community such as this. Reject (AKA, don't use) the things that are wrong, and create new things that are right to give an alternative (or entirely replace) the wrong things.
