Every post is a leaf in an append-only Merkle tree. Leaves are re-derived from post content on every checkpoint — never read back from a stored hash — so altering a post moves the root and every checkpoint published before it stops matching.
A log nobody checks is decoration. As Filippo Valsorda puts it, transparency logs are useless without monitoring in the same way signatures are useless without verification — and non-equivocation is something you cannot establish alone. An independent monitor is the next thing to be built here, and until it exists this page is the operator checking his own homework.