The reason taxonomic scientists must almost always take a specimen and deposit it in a collection is because it is impossible to be certain a species is new without having the actual, hard specimen to look at, and because hard specimens of all species in a group are vital for providing reference material to compare future potential new species against. Differences between species are often tiny, and require extremely detailed examination; far more than can be provided by digital photographs. They also need to be centralized in major collections in order to be accessible to scientists wanting to study these species. So normally there is no alternative to specimen collection. Calls have been made (including by Operation Wallacea scientists) to remove the criteria for a specimen where there is absolutely no doubt that a new species definitely is “new” from direct observations, but at least 99.9% of the time this just isn’t viable.
So, this raises the question of “is it worth collecting specimens if it means killing an individual of a new species as a holotype”? Which is a fair question. The answer to this, though, is most certainly “yes”. Taxonomic description is the first step towards effective conservation. If a species is not described, it cannot be given an IUCN Red List category, a CITIES appendix, or other conservation legislation. To all intents and purposes, a species doesn’t exist, legally speaking, until it is described, and thus cannot be effectively protected. So by taking a specimen just once, processes are put in place that can protect the entire population of that species indefinitely.
So, while specimen-taking can seem distasteful to some, it is a 100% vital part of the taxonomic process, and the taxonomic process is 100% a part of species-level conservation
And if you don’t describe a species properly, based on specimens, you can ultimately be endangering the entire population of that species.