> If I have a legitimate copy of the software I can use it, I don't need a license.
How can you have a legitimate copy of software without a license, assuming that the software requires you to have a license? You are simply using circular reasoning.
If someone puts their code on a web site like GitHub and invites the public to download it, then a copy made by downloading it there is a legit copy. I didn't agree to any contracts to download it and I don't need a license to use it. I do need a license to make copies or derivative works and distribute them. In this case the Copyright holder does provide a license to do so under certain conditions.
> How can you have a legitimate copy of software without a license,
You can because someone bought a physical copy, and then exercised their rights under the first sale doctrine to resell the physical copy. (With sales on physical media being less common, it’s harder to get a legitimate copy of software without a license then it used to be.)
How can you have a legitimate copy of software without a license, assuming that the software requires you to have a license? You are simply using circular reasoning.