Very ironically, understanding etymology today to be "true word meaning" is commiting to the etymological fallacy.
First, etymology is often uncertain and speculative, because speech in general. We can't be anymore certain about a words ancient usage than the scribe we learned it from. E.g.: The origin of Slav from slave is highly contested. Ignoring doubt in face of uncertainty would be fallaciou
Second, even if a word is well attested, at some ancient point in time, the way is often not clear that it took to arrive in English. E.g.: I have looked into "plague", found it refered to Latin plaga "wound", but no mention of where and when. That's not enough to work with. Accepting it as the last word would be fallacious.
Third, if a words development is well attested, we can be sure that the meaning has changed, or even come to be an auto-oxymoron. E.g.:
a) dysphemisms in recent times, like retarded, which was once a medical term, but now has been denigrated to a slur;
b) many Latin loans, e.g. camp, camping which didn't exist in that sense in classical Latin, but rather meant "open field, battle field, encampment", where part of the etymology transparently rests on the morphology, and part on semantic widening;
c) semantic narrowing is a thing as well, e.g. in car, cart, carry, as it's obvious that the definition for car today involves a motor; in that sense, motor, mecanismus etc has become polysemic.
d) figurative usage: a computer was a person only a century ago; The word for the computing machine only retains the animate aspect of the morpheme -er.
In these cases, it would be fallacious to stick to one ancient interpretation.
Fourth, in case of doubt it is often reasonable to assume that the core meaning of a word can still be inferred from usage.
- e) even if reinterpretation happens, so that the morphology of a word changes, or if the original etymon has been forgotten, there's often one context in which the original sense is retained, which appears paradox after the change. I'll owe you an apt example. Trivially, the more complicated roots of Latin terms are commonly not well understood, e.g. the difference between re- "back, again, against", res- "thing, matter", but this is mostly inconsequential, because ...
... It would be fallacious to infer diachronic etymology on the basis of corrupted morphemes and folk etymology. But it would be likewise fallacious to infer synchronic etymology from diachronic etymology.
If Karl means "king" in Polish, Schärler "fighter" in German, and Karl, Charlotte personal names, and churl "knave" in English, then that's just that
I mean other than semantics( or more subtle meaning, nuance) of what other use could studying etymology be.
Historical linguistics is important for history, in various ways.The reconstruction of Proto-Indo-European religiin is just one amazing example. But! The etymological fallacy means we can't rely purely on linguistic evidence, but have to work in tandem with the fields of History, Archaeology and even Geology.
Languages do Evolve but there can be no sudden or drastic Semantic changes.
See a) above. A similar timespan of ten to hundred years looks pretty much like an instant through the lense of history. A single utterance is basically an instance. An utterance may have lasting effects if it reaches many listeners.
I do not think I am a language purist just because I want to avoid ambiguity.
Mere passive desire doesn't make you an -istor of any kind, but being proscriptive, activelly denying certain meaning and usage does. Indeed, proscriptivity is often based on authority, but that's a matter of Socio-Linguistics. Etymology only tries to chronicle the development. Etymology can inform authoritative decisions, but that's often not the basis, see 1. above. Vice Versa, Socio-Linguistics can try to describe the politics of etymology, whereby the basic assumption is scientific rigor and good intentions.
PS: Your post is missing a direct question. It appears like a request for comments.So I picked out the last statement and interpreted it as a question.