Farsi or Persian

We have had this discussion in so many occasions and in our weekly meeting in Agora in university of Toronto and other places. And as long as I remember all the experts in this field including one of our members who is finishing his Ph.D in linguistics, have said that Persian is the English word for Farsi or Parsi. So you can NOT use the word Farsi in an English text. It is like saying: "I speak Franc'e or I speak Espaniol" , it makes no sense, you have to say I speak French or I speak Spanish. So why is there a growing trend of people including some Iranians, using the word Farsi in English texts? Some people believe in some conspiracy theories, which I wont get into. Today there was another case in Guardian News Paper in UK. Please please try to leave comments for these people or send e-mails to any one who makes this mistake else where and remind them of the correct word, Persian.