[Monkeyget]

Several contemporary settlements have been excavated: Nevalı Çori, Jerf el Ahmar, Mureybet. So we know what the houses, communal buildings and granaries looked like. Göbekli doesn't look anything like that. The location also reveals that it wasn't used to live, gather food or trade: It's built on top of a rocky hill without access to food or water. You don't extract 15 tons pillars, carve them and move them atop a hill to make things prettier.

The buildings themselves are the biggest proof. No roof, inconvenient and small entrance, holes to let the soul escape. The carvings found at Göbekli were also found on other sites which were associated with religion and death. One example would be the carving of vultures and headless bodies. Vultures which are associated with death and the ritual of excarnation: the floor of the buildings were made waterproof and sloped to allow the draining of bodily liquids. We know that people in that area would bury bodies without their head or even reopen the grave to remove the head. They also have been known to put plaster on skulls and keep the heads around.

[Gravityloss]

How about a fortress?

[dredmorbius]

My thought exactly. Might not want to stay there long, but as shelter from a raiding party, stocked with food and water, possibly with shelter for a flock, might be worthwhile.