(no subject)
There seem to be no reasonable motive for aliens to show up on Earth in flying saucers. It stands to reason, then, that aliens that have showed up on Earth in flying saucers are cloudcuckoolanders whose motives are completely arbitrary and ridiculous to us.
(more seriously, assuming there are alien species out there with a distribution of values even somewhat similar to humans, there is one reason they'd want to mix it up with Earth creatures: Sex tourism. Hell, considering how weird and unique we are as kinda-hairless primates some might even have a preference for humans. How many alien abduction stories can be read as sexual encounters again?)
(more seriously, assuming there are alien species out there with a distribution of values even somewhat similar to humans, there is one reason they'd want to mix it up with Earth creatures: Sex tourism. Hell, considering how weird and unique we are as kinda-hairless primates some might even have a preference for humans. How many alien abduction stories can be read as sexual encounters again?)