Is it OK to block political speech?

I've been talking to folks a lot these past couple of days about the potential legalities around blocking unwanted spam from non-profit, political or advocacy senders. From what I understand, this is pretty likely to be legal. The first amendment limits government action as it relates to restricting speech. But the first amendment doesn't apply to private parties; there is no constitutional "right" that private party number one must accept a message from private party number two. That seems cut and dry. CAN-SPAM certainly doesn't touch on it; it doesn't say a spam filterer can't block certain kinds of messages.

But, is it right? What if you run an ISP, or a blacklist, and you choose to list or reject mail from somebody sending mail with a political purpose? Is that ethical? Should it be allowed? I think that blocking that kind of mail should be allowed. I believe that it is the right thing to do. Why? Here's my take.

• Spam is spam is spam is spam. The reasoning behind it doesn't matter. The content doesn't matter. The amount of goodness in your heart doesn't matter. It's unwanted bulk garbage, regardless. If the recipients didn't ask for it, and you're adding them to a list and blasting to them, you're spamming, and blocking spam is the right, expected thing to do.
• Commercial vs non-commercial doesn't matter. If you're advocating your position to me, you're still trying to sell me something - your point of view.
• Disallowing ISPs to use their best efforts to block this kind of thing is kind of like forcing me to open my front door and allow you to bring your trumpet in and blow it in my face. Or forcing me to turn my TV on and have to keep it on the channel you specify.
• It's not like driving a sound truck down the public way with the speakers blasting ads for a political candidate. It's like forcing the truck into my private garage. My email inbox, and the ISP server where they reside are not the public way. They're private space, reserved for exclusive use of those who live there.
• It's not like "equal time for all candidates" in the broadcast media, ala the Fairness Doctrine. ISPs and spam filterers are not government-licensees of a public resources. The mail servers you and I are using at the ISPs you and I are using a wholly connected via private interconnected networks.
• It's not neighborly to send me garbage I didn't ask for. People have wildly varying political views. Forcing those views into the inboxes of people, many of whom are going to disagree with that opinion, isn't going to make you many friends. I'm already decided on whether or not I am pro-choice or pro-life; do you REALLY think your spam is going to suddenly get me to reconsider?

And whatever you do, don't tell me it's a political conspiracy when somebody starts blocking your political or advocacy mail. Spam filters block spam. The vast majority of spam filters are data driven and have much less to do with the content of what you're sending. Complaints and spamtrap hits driving a blacklisting or blocking issue have nothing to do with your political point of view and everything to do with poor list practices. MoveOn cried "it's a conspiracy!" back in 2006 when they got blocked by AOL, but their claims and whines were thoroughly and completely rejected by just about the entire world. It was a wasted effort, time they could have better spent on building their list SMARTER instead of just growing it BIGGER without thinking.