Blood-sucking aliens in the movies

Aliens after human blood

I think it is stupid when I see movies where aliens want to drink and collect human blood.  In the movies, aliens fly halfway across the galaxy in a cramped space ship; all because they want human blood.  There is no way that aliens would go to such great lengths to get human blood. 

I have seen four movies where aliens steal blood from people.  And in each movie the aliens never test the blood before they use it to see if it is safe to use or not.  That is crazy!  Blood is dangerous, people have: hepatitis, infections, diseases, and tattoos.    

It’s like these aliens haven’t discovered biology yet.  They can travel across galaxies, build laser guns, and translate any language.  But they don’t bother to stop and check to see if a person’s blood is safe to use or not.

The Food and Drug Administration protects people from bad food in the United States.  Don’t these aliens have a Food and Drug Administration that tells them the dangers of collecting and consuming human blood and tells aliens the precautions that need to be taken when dealing with human blood?