It can be very off putting to try and read something and find that the grammar and spelling are so awful the errors detract from your ability to understand the point. However, being over critical is not always the best approach. In my previous incarnation as a new/used bookstore owner, someone once brought in a book they had finished reading. When I opened the book, they had marked all the errors in red ink.
Sometimes though, you need to recognize that rules, once understood, may be broken deliberately.