But Freckafree, that’s the problem. The way someone writes is an indication of the kind of person he/she is. As you yourself said, if someone can’t string together a couple of coherent sentences, then that tells you something about the person.
Mind you, I’m not saying that one’s writing style gives you complete insight into another person’s character. However, it does tell you something.
Perhaps more importantly, when somebody exclaims, “Who cares about quality? You should be the one who strives to learn about the other person, instead of judging them based on the quality of what they wrote,” that says something as well. It tells me that this is a lazy person who doesn’t care about his or her work. Rather, this person wants others to make the effort to sift through his half-baked (and perhaps incoherent) ramblings, so that he doesn’t have to put his or her best foot forwards.