Personally, I don't think many if any people will go the extra step to start digging into files or installing other third-party software to solely get FOV, but if it's readily available on a 'legal' client, then obviously people are going to use it, which is the problem.
I agree, WFE2 FOV enhancer is undeniably a cheat and because it is so easily available it means a lot more people will be using it that normally wouldn't, of course that if you forbid it like any other prohibition (guns, drugs and e.t.c) there will be people commited enough to circumvent these rules but they will be a neglible minority.
Now the question is if you want everyone to have access to it, putting those who don't know about it or just don't want to download it at a clear disadvantage (pretty sizeable share of the playerbase), or keep an even playing field for everyone for the most part.