"Severus was mean to his students."
Ma'am, Severus was a man in his thirties with three jobs, responsible for teaching seven different year groups, grading their assignments and exams, performing his regular teaching duties, working as a spy for Dumbledore (constantly risking his safety and life to infiltrate the inner circle of the most dangerous man in history), working for the Order of the Phoenix, and keeping an eye on a group of reckless brats who spent 24/7 putting themselves in danger because they were incapable of accepting the word “no.” As a result, he constantly had to put himself at risk 24/7 to make sure they didn’t end up dead. And in the midst of all that workplace exploitation, for which he received literally zero incentives or rewards, those same kids, who had him at his wit’s end because he was already drowning in underpaid work, were the ones backtalking him, suspecting him, stalking him to see what he was "up to," or simply challenging him constantly.
I mean, it’s not that I don’t care that Severus’s treatment of his students was questionable—it’s just that I’m 28 years old, with a job, debts to pay, bills to manage, and adult responsibilities. The mere thought of having not one but two extra jobs, on top of all that, which also put my life at risk, and having to deal with the nonsense of a bunch of insufferable kids, honestly gives me major anxiety. So, I can understand why another adult, ten times more overworked than I am and with triple the responsibilities, wouldn’t have the time, patience, or energy to be nice to kids who either just added more work to his plate (Neville) or only contributed to his stress and frustration with their awful attitudes.
Severus wasn’t a poor, innocent soul or a victim, but he was a dysfunctional adult with an overwhelming workload and terrible working conditions who was completely fed up with everything. And honestly, no one can understand that better than other dysfunctional adults with too much work, low pay, and a similar level of frustration with life.