You have used a different set of rules to derive the "snarkophilus anti-catastrophe", namely, that humanity will never become extinct, because each total number of humans greater than our present birth number is equally likely, and there are a virtually infinite number of possibilities! Interesting. This seems as justifiable as the Carter catastrophe if yours are in fact the right rules, but really neither set of rules are very plausible, just as the "everything has a 50/50 chance, it either happens or it doesn't" is also not a very useful rule. What do you say to the alien time traveller argument, in relation to your picture of the right rules?