A guy complained about you spamming him and then you spam him on HN to promote your conference? You really don't understand your demographic.
Of course they should be able to do so, but chasing someone down who has (publicly, implicitly) expressed a desire no longer to be contacted, and for whatever reason making the contact in a forum in which it does not belong ("sorry if it was unwelcome" arguably belongs here; "how can we make it up to you?" belongs, if at all, in private communication), it seems to me is an unsavoury tactic.
If you read my bio, I think you'll see that I understand the demographic quite well -- http://about.me/Edro