In some of my college course work way back when, I was required to know how to prepare study skins of birds (the institution was allowed to keep such specimens, hence we were allowed to work with them in our capacity as students). I also learned the same for mammals at the same time. Some time ago, I posted a now-closed thread on the lost macaws of the Caribbean, which emphasized that, although there are thirteen proposed species, many are disputed due to the absence of physical remains as specimens. The Cuban Macaw is the only one whose plumage pattern we can be sure of, because it is the only one with extant museum skins.
And yet, I find myself at a point now where I cannot bring myself to kill any animal for a specimen, not even an insect or spider. It may be, as @annainok said, “hardly a drop in the bucket;” but the real difference is intention. Inadvertently killing an insect while driving is not the same as intentionally killing one, aside from any question of numbers. I arrived at this point as a result of being a vegetarian for many years; it was a gradual process.
Plants are different, in that they lack a central nervous system.