Two of the most foul and arrogant words in the human language are "Nothing but". Those words assume that the speaker knows absolutely everything about the subject. I have heard them used by scientists, magicians, scholars, and know-it-alls, alike.
"Nothing but" tends to remove any personal relevance of the thing talked about.
Example: "Love is nothing but a neuro-chemical reaction, similar to eating large amounts of chocolate."
I've also seen psychologists and materialists use it to explain away religion and mysticism.
I've seen mages use it to explain away the practices of other mages, witches, and mystics.
It's that last bit that annoys me most. Someone who doesn't believe in anything at all that isn't physical matter or energy does have a narrowness of paradigm, but it's so narrow I don't especially blame them. They've simply had no experience of the subject matter, personally. Or if they have, they choose to interpret it through an alternate lense.
A know-it-all practitioner does the community a disservice, by claiming an almost pontifical, objective knowledge on something that is so intensely personal. It also sets a mindset for a "One True Way", which turns my stomach in a way that few things do.
They also do themselves a disservice by never even really considering another position as valid. They entrench themselves in a solid belief, and view their reality map as reality itself; admitting anything not within their map, or translatable to their map as either non existent, wrong, or sadly misinformed.
The same "nothing but" arrogance also lends itself to the phrase, "If I could explain it better, I know you'd agree with me." Assuming that you are without a doubt correct in your view, but likely the person you are talking to is sadly far too dull witted to understand the high concepts presented. Oh, it's put very politely, but it is still a statement of superiority, coated in a false humility.
Words help shape our reality, thus we should phrase even our internal thoughts deliberately, to enable us, to inspire us, and to keep our minds from falling into the dead end of know-it-all absolutism.