Humans should have more legal privileges than machines, just as individuals should have more legal privileges than corporations. It's really as simple as that. I don't want to gripe around making up justifications, that's how the law should be and if it turns out not to be that, I'm going to be nettled.
I live in the UK, and most US law is based upon English common law, it's not some immutable code given to us from above. It's based upon assumptions and capabilities of the entities participating in the system at the time the law was codified. It can and should change to make more sense if those assumptions and capabilities shift massively.
I get the individual/corporation distinction, but how is a machine another tier here? It's a tool, it can't have any rights at all. The wielder has rights, and curtailing their rights depending on what tool they're using to exercise them seems strange. Potentially justifiable, but it's a different axis from the nature of the actor.