> consistent rule-application on a mess (blocks with utter garbage) would still yield the same results among everyone that applies those same rules
From the perspective of a bitcoin node, the entire internet, other than the tiny sliver that constitutes the bitcoin blockchain itself, is "blocks with utter garbage"
If you tried to serve the entire internet to a bitcoin node, the only parts it would validate are the blocks that constitute the bitcoin blockchain
It ignores the rest -- the mess, the junk, the utter garbage (from its perspective)