>It's better to communicate as an individual, warts and all, than to replace your expression with a sanitized one just because it seems "better."

It is definitely not true that it is better for a poster to communicate like an individual when it comes to spelling and grammar. People ignore posts that have poor grammar or spelling mistakes, and communications that have poor grammar are seen as unprofessional. Even I do it at a semi-subconscious level. The more difficult or the more amount of attention someone has to pay to understand your post, the less people will be willing to put in that effort to do so.

Exactly. Tell that to whoever is grading your next paper, or reviewing your resume, or watching your presentation. People are judged by their linguistic ability even in cases where it shouldn't matter. It's a well known heuristic bias. It's no surprise that many of the people here denying it are themselves quite literate.