Keeping it spread out across millions of individual home computers, laptops, and mobile devices is the strongest, and perhaps only defense of that.
If you want to argue, at least argue the real issue, not some strawman.
It's all moot though, because introducing sidechains and the lightning network destroys the value of Bitcoin in a perverted attempt to save it from a non-existent problem.
> Keeping it spread out across millions of individual home computers, laptops, and mobile devices is the strongest, and perhaps only defense of that.
No, because Bitcoin was built to be resilient to Sybil attacks, that's why it's proof-of-work and not proof-of-stake. So it doesn't matter if a million people in Africa have the whole blockchain on their raspberry pis or laptop or whatever, because all I need is one ASIC mega-farm in Antarctica and I can double spend attack the network into oblivion.
It's hashpower that protects and secures the network, nothing else. This is one point that the fraud CSW actually got right.
Having many independent observers seeing the entire chain and detecting problems or attacks against it, facilitates coming to consensus out-of-band about what's happening and what to do about it. It's the ultimate check-and-balance.
The whole idea in their heads is that nodes will "validate" transactions. Which doesn't make any sense because it's the person engaging in a transaction (on either end) that cares about the state of the blockchain, not some random neutral third party. Your full node can detect an invalid transaction all day but without a way to tell the guy who's about to treat that invalid transaction as valid, the utility isn't there.
No, the real threat to the Bitcoin network is and has always been that a hostile actor would get 51% hashpower (or almost 50% but not quite and roll the dice until they won a few blocks in a row) and issue double-spend attacks.
But fwiw the technology does exist now to do that, just in another protocol: