The Chicxulub impactor: comet or asteroid?

A recent paper by Siraj & Loeb (2021) entitled "Breakup of a long-period comet as the origin dinosaur extinction" attempts to revive perennial debate about what type body hit Earth 66 million years ago, triggering end-Cretaceous extinction. Here we critique and assess evidence it presents. To consider more likely than an asteroid requires extreme assumptions how comets fragment, conflation carbonaceous chondrites with specific types chondrites, blind eye iridium layer.