You seem confused about the definition of copyleft. When something licensed to me under, say, the BSD 2-clause license, I have the ability to look at the sourc

You seem confused about the definition of copyleft. When something licensed to me under, say, the BSD 2-clause license, I have the ability to look at the source, to alter it, and to redistribute it (with or without modification). It is not copyleft, because it does not require that derived works be released under a comparable license.