As a (pretend) Zoologist, I have a few thoughts about this.
The fact is that in this case, the scientist was acting in accordance with majority scientific opinion. I’m not defending his actions and clearly the outcome is tragic, but it is likely that photographic evidence alone might not have been accepted as definitive ID in this case.
As an amateur entomologist I choose not to take voucher specimens precisely because I do not know the size of the population I am sampling from and so cannot predict the consequences. In the above case, the population size was known and the consequences were predictable. However, with many species requiring microscopy for accurate ID, not taking specimens makes me less effective as a wildlife recorder, and likely to miss rarities which I cannot positively identify in the field.
In general terms, there is no easy answer to this one. In specific terms, in the above case the wrong decision was made.