The key for a coach is clarity, honesty and consistency; the former in setting out his expectations to the squad before the season - and presumably Blackadder has stated that anyone, regardless of status, will be dropped straight away if they do not come up to scratch - and honesty in explaining his reasons for the decision. Now Blackadder must follow through with this policy for the rest of the season. He has to be consistent with his decisions and with every player.
Dagg didn't have his best game against the Chiefs - he lost possession in contact three times - and wasn't the attacking threat the Crusaders required, but none of their backs looked consistently threatening and he did appear to be trying hard. Reason enough to be dropped without having another chance? Only Blackadder can answer that.
Kirwan said Noakes didn't take the news of his demotion well, something the coach said he expected. Looking at it from the outside, it's not surprising he was disappointed. He didn't play well in the first half, and while he would have been expected to give his side, which looked in disarray, direction, he looked a lot better in the second half once his forwards began showing a little more intent.
One of the foundation pillars for any team ethos is the "team first" mantra, in which everything is done for the good of the team. It is a convenient one for coaches too. If "no player is bigger than the team" then coaches should be able to select who their want without players responding poorly.
The big danger is that too many selection disappointments can spread from player to player like an illness. Coaches have a responsibility to manage players, to get the best out of them.
It is a difficult balancing act and one only a select few can do well.