Some professors grade on ideas while others look for grammar and spelling. This can be confusing because students may not know on which area to concentrate. It's difficult for freshmen who may not have one or either of these writing skills perfected. These misspellings create the image of the writer as less intelligent and less careful, even when such is not the case. While subtracting points for spelling errors on a test is not perfectly fair, it is sensible because it combats spelling problems.
Many resources are available to overcome spelling errors.
Because of these resources, and the awkwardness of spelling errors, they simply should be eliminated. It is important to be grammatically correct, but grammar should not be the main focus of attention. The ideas expressed are of more value, and from personal experience, if I am worried about getting marked down for grammar errors, I tend to focus on my grammar rather than think and create freely. Worrying about grammar inhibits creativity. Spelling incorrectly is just as bad as having a run-on sentence, punctuating incorrectly, or forgetting to capitalize.