It is human nature to judge people for whatever types of work they produce or how they present themselves. Language is often a form of what it judged--often the written form.
It’s funny; I just had a conversation with my dance instructor less than an hour ago about how unprofessional dance websites and emails appear because the spelling, and sometimes grammar, are so bad. Often, it’s easy to see errors in documents as a form of laziness, which directly funnels into a perception of the one making the errors as unprofessional. For these reasons, judgements about errors are valid, but to an extent and in context. If a document that should be professional is riddled with errors, that reflects negatively on whomever wrote it, and rightfully so.
Alternately, one could argue that errors are no big deal if they don’t inhibit clarity. Larry Beason discusses this in his essay/study, “Ethos and Error.” For example, I am in Chicago right now at a dance event--the very event that sends out the atrocious emails that were part of the conversation I mentioned earlier. Do I find the emails annoying and unprofessional? Yes. But do they stop me from coming to the event? Nope. Somehow--and it takes some effort to do this--I must realize that there are more important things to consider about going to a dance competition than how professional and correct their emails are. However, if there were many other indicators of laziness or unprofessionalism that stained the name of the event and its directors in addition to the emails, that would be a different story.
One could argue that sometimes we are too critical and judgmental of people who do not place a high priority on correctness. That may be true, as it’s easy to be a stickler--even borderline pretentious--when it comes to making judgements of people about their writing and the errors within it. It’s another way that we find to pass judgement. Really, like anything though, it’s a matter of considering context and keeping things in healthy perspective.