Even ignoring the first amendment, there is no enabling clause that grants the general power to regulate communication.
You may have the right to speak but you don't have a right to force the populous to listen.
Communication is two way, spam is one-way.
You have the right to expose people to communications with no Congressional control whatever. Congress shall make no law. You may shout on a street corner, you may set up a PA system until your neighbors are driven to madness, you may place pornography on a billboard, etc. Congress can do nothing to stop it.
Are you trolling. You consider the constitutional right to free speech to encompass things like setting up a PA in public that is so loud it physically harms people?
It's not a right to amplified speech, nor "free shouting".
Freedom of speech does NOT involve the freedom to send individually addressed messages to anyone. There is no freedom to spam.
CAN-SPAM doesn't apply to political or non-profit organizations.