Is it a very bad idea to write xor in an article?

You are writing an article in English. Therefore, sentences should only contain correct English words, and not some combination of terms you would use in formulas and normal English words. Therefore, I would strongly recommend to use

either ... or ...

Also, if you are using XOR, you should write it in all-caps (Sources: Oxford Dictionary, Merriam-Webster) which makes it less attractive to read it in most sentences.