What many free software advocates actually want is a world without copyright on software. It's copyright that frames copying as stealing. In a world with copyright, the only way to counter that is copyleft. The fact GPL can also enforce inclusion of source code is a nice side effect of copyleft. But ultimately what we want is a world where software is shared, treated as knowledge and not as a product.
MIT style licences are just not good enough. That software could still end up in some copyright protected proprietary product one day and then, yes, someone could accuse me of "stealing" their property, which contains our software.