Humans tend to dehumanize those people who they do not like. Enemies are "demonized", "made a scapegoat", and so on. These are interesting sayings because they show the non-human status of the referenced people. The derided are given a status less than their accusers. Indeed, the extreme guilty are cast non-human, unworthy to share the stage of "real people".
Discomfort occurs when people are forced to consider the formally dehumanized people in a different light. Things are really shaken up. The acknowledgement of a person's humanity can be very uncomfortable if their previous status was less than human.
I'll share an example. Let's say a person sees a particular lifestyle as an "abomination". The person believes that those who practice the lifestyle are unrepentant sinners who richly deserve the punishment of the divine. A nice couple then moves in next door. They are polite, courteous, caring, and "good people". They also practice the inhuman lifestyle. The thought of the neighbors being condemned to an eternity of suffering becomes uncomfortable. The recognition of the neighbors as possibly human takes the 'zing' out of the larger inhuman judgment of the lifestyle practicing group.
The risk of not labeling these neighbors as "abominations" opens the door to accepting that like others may not be inhuman either. The bedrock of inhuman classification is potentially shaken for the prejudiced individual. Let’s say the person then finds out that others around them are also practicing the sinful (and hence inhuman) lifestyle. Can the individual honestly say, "my neighbors, child, co-workers (assuming they have the same lifestyle) are OK even though they are an abomination, but all the others are hedonist sinners craving the punishing embrace of the afterlife"? The doorway is open to bigotry and a form of moral "Multiple Personality Disorder". The cool comfort of inhuman categorization is replaced with the very messy business of dealing with people as relative equals.
It can be a messy business to deal with other people as equals. If we face ethical, moral and cognitive challenges while seeing disliked people as 'human', where does this leave us when we relate to machines in a way that grows closer to humanness? Ah... a topic for another day!