Debunking complaints about the ending of Indy 4

SPOILERS below, for those who care.

Why are so many critics complaining about how ridiculous the ending of Indiana Jones 4 is (examples here, here, and here, for starters). Is the notion of Martians populating the Earth really that much more ridiculous than the Ark of the Covenent releasing eye-popping demons, voodoo doctors and monkey brain eaters guarding legitimately sacred stones, or the Holy Grail? Once you've crossed the threshold into fantasy, who's to judge which is more ridiculous than the other? Are the Judeo-Christian myths that more "realistic" than the Mayan myths?