When you preface your comment with "Unpopular Opinion", then proceed to make a sweeping assertion like "The purpose of education past 8th grade is to keep young people out of the job market", without any supporting evidence, that's what we call "inflammatory rhetoric". This kind of comment will always attract downvotes and flags. This style of commenting is against the HN guidelines, as is complaining about downvotes.

The correct response to downvotes is to think about how you could express your point in a way that people can connect with. That's the art of a good comment. The best comments on HN are ones that make a point that many in the community may have disagreed with, but it is expressed in a way that creates a pathway for people to see things in a new way, and persuades them to see the issue from the new perspective you're illustrating.