Although some versions were released for free, and Apple may have entered into arrangements to allow others to redistribute the software, that does not grant me the right to redistribute. In fact, the license for System 7.0 explicitly forbids what we're talking about, under section 2: "You may not electronically transfer the Software from one computer to another over a network."

Additionally, my own license to use the software is terminated under section 3 if I were to violate section 2, and I would be obligated to destroy my copy in addition to any other liabilities I (and anyone else) would be exposing myself to by violating the license and any applicable copyright law.

IANAL, and some may be willing to accept any potential consequences, but if the forum knowingly facilitates or encourages the violation of copyright law, they expose themselves to liability as well. Which is why the rules exist.