Will be described in more detail later but the culture of Demon society is a cold pursuit of benefits. Lizel, Raina and Miyabi are outliers as caring individuals while most demons are like Gelt albeit more cool headed. Basically it's considered counterproductive and foolish for a parent to raise a child with parental affection. Culture is parents 'invest' and raise the child with the hope the child will look after them when their old, and bring money, power, position, and benefits to them and their house. The child isn't to expect love from their parents but work hard to gain favor so parents will invest in them. Also, to avoid 'bad' influences or ideas from taking root in a child they are raised away from humans. Hence typical Demons only care about themselves and what benefits can gain. As for referring to humans as livestock that's because Demons can turn some of the energy given off by strong emotions from humans into power for themselves. As Lizel mentioned many demons like to use power and fear because it's easier, cheaper and quicker to bring forth negative emotions than positive ones. That and they can pamper their own egos with how great they are by exploiting and abusing humans with excuse that weak can only blame themselves for being weak, exist only to benefit the strong, and are an inferior species. As a result of these ideals over the course of centuries have brought forth the negative view of Demons by humans. Demons aren't native born on the human's Earth but come from another world.
Don't know if Demon world in same universe (albeit really far away,) or in a parallel universe but only way to cross is either through a gate connecting the two worlds or a dimensional tear that occurs for some unknown reason causing those who fall in to either die or get spirited away. Gates are either heavily controlled and secured by the government (considered a high class luxury to go from Demon World to Human World,) or owned by Demon families with long history and high standing who found/made a portal between the two worlds before all the regulations and restrictions were put in place. In LN what little of Demon World shown is a lot like Human World but with magic and monsters outside the secured areas. So similar to going out in the woods outside town and little chance of encountering wolves except for certain areas, and wolves would have magic to make them more dangerous and stronger than the Human World versions. One area/section(?) of the Demon World is known as Purgatory where Demons who die in Human World are forcibly taken to and can never return to Human World again. Unknown if injuries from dying are healed in transition or to what extent but implied will still be alive when get there. Conditions seem to be horrible there and while a Demon who hasn't died can find and meet with a Demon who died in Human World there it's suggested that doing so is extremely difficult. Even then the Demon who died can never return to the Human World although details on why haven't been explained yet.