If copyleft means restricting freedoms on what you can do with software and preserving those rights on derivative works (GPL) - then 100% no, those people need

If copyleft means restricting freedoms on what you can do with software and preserving those rights on derivative works (GPL) - then 100% no, those people need copyright laws to enforce that. With no copyright law I could take any GPL software, modify it, sell it as my own and nobody could force me to give up the code. If copyleft means permissive (MIT) - then it's not a hostile environment. You are free to create and share permissive works with no hostility from anyone else.