That isn't a legal constraint, it's a physical one.

Sure, but the founders didn't bother clearly deliniating all the physically impossible ways the government shouldn't be permitted to violate our rights. It is quite possible that something newly possible is a violation of rights we were supposed to have, whether specified implicitly, explicitly, or not at all.

At an extreme, the constitution says nothing explicit about brain control rays, but if we invent them I am quite confident in asserting that use should be deemed unconstitutional because of rights we should be assumed to have.

And?

I think that is actually very relevant.

For example, if I scrape email in an automated manner and send messages to those emails for purpose of profit (say, advertising my business), then I am subject to very different laws regarding spam than if I manually gathered the emails.

I'm sure, given your legal prowess, you could expand a very interesting argument here. Ok, your turn ;)

And there is a substantive difference between surveillance and mass surveillance. It's not just a matter of degree; it's a matter of kind.

And the 4th amendment doesn't say anything about either. The fact that something is bad doesn't mean that the Constitution provides some means to make that thing illegal.