absolutely -
It is part of human nature to love and have compassion for others - although this is a weak comparison - its similar when people adopt a pet -- Not that an adopted child is a pet -- that the adoptive family often love their pet as a member of their family, care for them, nurture them, play with them, help them when they are ill, and grieve them when they pass away.
Yet this O.P. implies that none of these feelings are inside of his adoptive parents.. Thats a tall order right there.. Again-- it is possible that they are monsters, but I have the feeling they love him more than the average family loves their pet -- that they love him as much as any parent loves their children- and to rebuke them this way shows me just who the monster is.