I'm not sure that I follow everything you've written, but I'll try...
alfred1 wrote:given that luckily or unluckily (depending on one's point of view) we still know very little about groundwater fauna...
We know terribly little about pretty much everything. While we have a responsibility to the things around us, our overwhelming ignorance, and the measure of harm it will inevitably cause, are no reasons to abandon what learning tools we have at hand.
alfred1 wrote:considering that fluorescein isn't that toxic but also not exactly harmless (more data on this can be spilled later, even if AFAIK there is nothing that conclusive about invertebrates toxicity), is it really that important to potentially sacrifice unknown living beings with unknown distribution and population number, just to dye a load of cubic meters of water upstream to see if they're dyed downstream?
I wonder why you're so concerned about this if there is as yet no concrete reason to suspect fluorescein as harmful. But to answer your question is impossible. You're asking us to pick one sort of science (which is only another word for learning) over another. Is groundwater biology inherently more important than hydrology? It depends on who you are. Traditionally, as you've hinted, the people using fluorescein in caves and springs have been cavers. The movements of underground water are often the key to understanding cave systems and the key to discovering more cave. These things are more interesting to many cavers than whatever critters live in the water.
alfred1 wrote:Are we being over-enthusiastic into using it just because one can personally buy a bucket-worth of dye with his/her own wallet and head out of the store with still some cash left, or would it be the same if we used more expensive tracers?
Of course we'll use whatever is most accessible and does the job. If, for example, the price of fluorescein increased dramatically, many would quit dye tracing, and some would resort to other mechanical (paper chads have been used) or definitely harmful (dish soap has been used) means.
alfred1 wrote:some researchers either think only about their own field, for example geology, and forget about everything else
Many researchers have a narrow focus. It's what allows them to get things done. Does it lead to negligence in other areas? Yes.
alfred1 wrote:...hoping this will leave a mark into our community
This comment about motivation may or may not be accurate. Ego often plays a huge role in exploration and discovery, but so do other things...
Having mostly withdrawn from what little involvement I've had in the "caving community", I find my own eagerness to explore, to walk and map and dig and find, that is, to learn
, is undiminished.
Or, to answer your questions another way...
In SW VA is a cave that I have come to know nearly as well as an amateur can. One of the remaining mysteries is that of the large cave stream, which sumps in a deep pool nearly 100' above the local water table and nearly one mile from any significant known resurgence. I think of this pool very often, but I am not a diver, and am probably too timid to ever become one. The only way for me to know this cave as completely as I can is to walk the land, and probably to perform dye traces. Will the (tiny?) possibility of affecting cave life prevent me from performing a trace? No.
I know that tiny things, within and without caves, are killed by me in the course of my routine living. I have made efforts to see and to know what sorts of things I am killing, and what sorts might live in this particular cave stream. While I cannot, and do not wish to, escape from involvement of life and death in this world, I desperately want to avoid haste, ignorance, and waste. Not all death is waste. Some of it is sacrifice, and if sacrificed honorably, adds weight and richness to our acts.