The readers are not telepaths. Correctness and clarity of written language on the forum is essential for the writer's ideas to be communicated in unchanged form. If the reader cannot comprehend the writer's meaning due to spelling and grammar errors, then the post was wasted space. If the reader obtains an incorrect or incomplete understanding of the writer's ideas due to spelling and grammar errors, then the post was wasted.
It's only different in degree to making a post in a language other than English, and then wondering why very few people respond to the ideas contained therein.
Besides, spelling errors and improper grammar look bad, are inconsiderate of the reader's time (it's enough work as it is to read the post and try to understand the idea, but to have to decipher the post before doing either?), and are something we would expect of an uneducated or illiterate Democrat. But I repeat myself...
I'm with you. I'll take it one step further and say that another practice that slows down comprehension is using alternative spellings and clever nicknames.
Example:
Clinton appointed twenty-four friends of Hillary and five other Democrats to the travel office staff.
vs.
Klintoon appointed twenty-four friends of the Hilldebeast and five other dummy-crats to the travel office staff.
The former might not be as much "fun", but it is easier to read and quickly comprehend.