I am conflicted in this, I think Holland could have handled the situation differently (player management) but it is not his job to make players happy but to ice the best team he can to win the Stanley Cup. Some players need different types of motivation (different type of society than 30 years ago) and it is the coaches or managements best interest to get the best out of player's they have brought in.
Also, as an individual you have chosen your pathway of gaining employment in this world. Slatter worked his way up to becoming only a few % of people to play in the NHL. Maybe, he stalled at this point and realized he was not going to be there long term. If he was not cut for this mentally, there is a long list of people not making it other professions. I hope the best for Slatter and hope he finds his way.