The above sentence appeared as an example sentence in a section of "Du's Handbook" that said the character 爲 (위) was sometimes used to mean "because of," but if that were how 爲 was used here, it seems like an awkward way of writing it, separating 不 (불) from the verb (易 - 역) it negates. Also, where is the translation of 而 (이)? Instead, wouldn't it have been much clearer to write the sentence as follows?君子不爲小人之匈匈而易其行“The superior man does not change his behavior because of the clamor of petty people.”
The 而 (이) in the original sentence was normally used as a conjunction to connect two clauses, so that would suggest 爲 (위) was used as a verb, not as the preposition "because of." In my Korean dictionary, one of the meanings of 爲 is "생각하다," which means "to think [about]," "to give thought to," or "to ponder," therefore, I would like to suggest the following translation:君子不易其行爲小人之匈匈“The superior man (君子) does not (不) change (易) his (其) behavior (行) because of (爲) the clamor of petty people (小人之匈匈).”
The character 匈 (흉) can mean "clamor," so using it twice either suggests a lot of clamor or helps to clarify the intended meaning.君子不爲小人之匈匈而易其行The superior man (君子) does not (不) give thought to (爲) the clamor of petty men (小人之匈匈) and (而) change (易) his (其) behavior (行).
For context, here is my translation of what seems to be the passage from which the sentence came, thought it is slightly different:
天不爲人之惡寒也輟冬, 地不爲人之惡遼遠也輟廣, 君子不爲小人匈匈也而輟行. 天有常道矣. 地有常數矣. 君子有常體矣.Heaven (天) does not (不) give thought to (爲) man’s (人之) dislike of (惡) the cold (寒) and (也) end (輟) winter (冬). The earth (地) does not (不) give thought to (爲) man’s (人之) dislike of (惡) vast (遼) distances (遠) and (也) end (輟) vastness (廣). A superior man (君子) does not (不) give thought to (爲) the clamor of petty men (小人匈匈) and (也) then (而) end (輟) behavior (行). Heaven (天) is (有) always (常) systematic (道矣). The earth (地) is (有) always (常) fixed (數矣). [And] the superior man (君子) is (有) always (常) himself (體矣).