on Writing Forward:
Homophones are words that sound alike but have different meanings. Many homophones also have different spellings, and all too often, people mix them up.
The result is an onslaught of misspellings throughout the written universe.
Although these mistakes are understandable, they are problematic since they are contagious. If someone sees a homophone used incorrectly or misspelled enough times, they will assume the usage is correct and adopt it.
Thus the errors spread.