You made a wrong factual assertion 2 posts above that one, and when someone corrected you by mentioning the Apollo missions, you didn't take the few minutes on Google/Wikipedia/whatever to learn about the subject, but instead repeated your mistake. It's appropriate for a comment of that sort to be at 0 or -1 karma; it's not like you got slammed to -17 and silently banned for egregious wrongitude. Think of the downvotes as encouraging different behavior: if someone gently corrects you, take the time to look up the information they mentioned.

(For the record, I did not downvote either of those posts, and I've upvoted some of your comments in the past.)