Was the visitor plan really a long-term solution?
Assuming for a moment the population on their home planet was close to ours.....how could their plan really be a long-term fix as far as food goes? Even if they grabbed every last person on Earth, would even that amount of meat last? Lets say you get 100 lbs of edible food per human (sorry if I gross anyone out here)....if they eat primarily meat, they would easily go through that in less than a year. Maybe they intended humans a supplemental food source. (Martin called food a "shortage" on their world.)
Unless they intended to breed humans (like we do with cattle, chickens, etc.), I don't see how their effort is worth it (putting aside the water for a second).
Ignoring: MythicCDXX, Creeping Jesus/Judas, RonPaul_Lies, Digby (and aliases), ibestupid, Holiday_Hobo, sharon_18, TilaMoo, Okie-from-Muskogee/boo321, NorCalNik, Nullifidian