My first instinct is it's people who have a high threshold for pain who don't appreciate being called out for a lack of empathy. But perhaps didn't have a rational defense to jump in and comment.
It would be interesting to hear a response from a downvoter contradicting this instinct.
More likely, the people doing the downvoting have low thresholds for pain and do not want to see people with low empathy become normalized, as it would make their pains feel even worse.
It would be interesting to hear a response from a downvoter contradicting this instinct.