And let's not forget graffiti and the camp "campi" as the plural of campus.

My question is, Once these words enter English, how obligated are we to follow the original language in pluralization - or, for that matter, any aspect of their use, including their original meaning? We agreed among ourselves centuries ago to communicate in a language not burdened with fourth declensions and such, so why are we occasionally fixated with these in Modern English?

Tangentially: Biological taxonomic names at the genus level and below are considered Latin words and are (well, should be) treated as such; above the genus level, they are treated as English words (or the vulgate of any country) and, despite their clear Latin and Greek origins, there is no non-Ehglish grammatical structure applied to them.

"I don't know which is worse: ignorance or apathy. And, frankly, I don't care." - Anonymous