That is the problem with written communication.
I think, as annoying it may be, your warnings may be needed.
I am a very sarcastic person. I am a very blunt person. but thats hard to determine a difference in written word. i've run into much the same problem as you. My way of speaking, my tone, tends to be interpretted wrong in written word. I've had many an issue here because of it.
I tend to preface my generalizations with- "In my experience I've seen ___". Still a generalization, but one based on my experiences.