Those cases have also spawned complex, multifactor tests applied by a government bureaucracy to restrict many entities and forms of speech. There are different rules for over 70 different entities, from corporations to partnerships, and the FEC has varying rules for 33 different forms of political speech. Those exceptions mean that while some corporations are prohibited from engaging in political speech, others are not. While General Motors is prohibited, General Electric, which owns NBC and MSNBC, is not because of the exception in the law for political speech by media corporations.
"Congress shall make no law ... abridging the freedom of speech" is such a pleasantly simple statement. Easy to understand. That's what I like about the Constitution -- it's short and to the point -- and hate about modern law, which is pretty much incomprehensible to everyone. :/