I feel obligated to point out that the comment you replied to never said anything about brightness control being built into any OS. They only found it humorous that someone would pay extra for it (presumably because it's free). Then... you went ahead and supported their argument by pointing out that it is indeed free; while also chastising them.

I guess my point is that your reply didn't really contribute anything to the conversation other than hurling an insult at the commenter for their past comments. Maybe they really just wanted to make a joke? On some level it would be silly to pay for something that's free, right?

Given that you're the original author, could it be that you may have replied as a defense mechanism? At least to some degree? If so, is that proper?

Honestly, I don't have a "dog in this fight". I just thought it was an interesting situation.