G'day guys,
There's absolutely no advantage jumping down Belgrael's throat about killing this Keelback. Whilst I definitely don't support killing native wildlife, the impact on Keelbacks as a species is nil and Belgrael has done what most snake killers don't - educated themselves (albeit a little too late).
By abusing or ridiculing those who kill native wildlife out of ignorance, you will do nothing but convince them that we are a pack of bleeding heart, vigilante creepy crawly lovers and give them even more of a reason to do it again in the future. What you need to do is understand where they are coming from - most people have a very legitimate fear of snakes and an exagerated perception of what they are capable of - and explain why the snake is there, the reason they aren't in any danger and give them alternative options if they happen upon another snake in the future.
Belgrael - as others have said, the snake you killed is a Keelback, or Freshwater Snake. They are completely harmless, and very common. Regardless of what species of snake it was (Keelback, Brown, Taipan etc), you are not in any danger. Be careful not to corner a snake, always give it an escape route. The biggest thing to remember is that snakes react to movement - if you stand perfectly still, no snake will show any defensive behaviour towards you. If you have enough time to grab a shovel to kill it, you've got enough time to go inside and grab your phone and call a snake catcher. We personally know several snake catchers in the Cairns area - if you happen upon another, give us a call and we'll get someone to come and grab it for you.
Cheers