That's the whole point and philosophy behind the GPL. That's why it's called "copyleft". It's about taking copyright law as it currently exists and using it subversively.
The person you're talking to is missing that point because they're starting at "freely copyable", while the actual default is that code is never published at all. GPL is compromise to push source code 90% of the way to "freely copyable" because the alternative is usually 0% copyable.