That's not what who is saying?
You consistently refer to some entity (in this particular case, one that is apparently capable of saying things) you call "I." When called on it you say it's merely a linguistic convention.
Okay, then explain how that linguistic convention applies. Use as many words as necessary to explain exactly what you actually do mean when you say "I."
There's no problem with using "I" to communicate. It's a well-established social convention. Problems only arise when you believe that there really is an "I" that is observing or experiencing.