I've encountered more than my fair share of amateur writers who are really resistant to the idea that their draft manuscripts should be proofread and error-free when they're pitching.
It used to shock me, but it doesn't anymore. Yes, there are lots writers who honestly want to approach mainstream publishing but think editing and proofreading isn't an important part of their job.
I think this opinion might come from the misconception that editing is nothing but running a spell-check program, even though they probably know on some level that it cannot catch everything. The real problem is that they think "spelling" is the only important part of correcting errors, and they think "correcting spelling" is basically not necessary for the artist to trouble themselves with. Don't they have literary janitors to do that?
Yes, when you are published by a publisher who pays you for your work and handles distribution of your materials, you are generally assigned at least one editor, and they do comb through your book to correct errors and make the text conform to their style guide. But that sort of treatment is granted to authors who do their job well enough to get to that point. And you can only do that by treating your material like form is as important as content.
Nobody in publishing wants to hear that editing isn't your job as an author. Nobody in publishing accepts that it's the story that matters to the point that you shouldn't have to fix the spelling and grammar errors. If you know you are not good at it (or you think you are but everyone else tells you you're not), what you do is get someone to proof it for you, not stomp around insisting that this particular part of making a readable product just isn't your responsibility. That would be like saying a musician who plays and sings poorly is deserving of major record labels' attention because the messages of their songs are so vital. That can be true in isolated incidences--that one part of something is so important that the usual standards don't apply--but it's not up to you to identify yourself as the exception to the rule. If you want the respect and attention of people who pull the strings in this industry, you need to play by their rules to the best of your ability. Most people who think their work is so world-shaking that they should be allowed to break all the rules right out of the gate are mistaken anyway.
Also, using correct spelling and grammar is not just a preference of pedantic whiny-babies. If you mix up your words and spell things wrong and fail to use punctuation, you really do make your work more difficult to read, and it pulls readers out of the story to focus on your words. You want it to be effortless for them to read. You want them to get lost in it. You don't want them to actually get lost.
It is your responsibility as an author to deliver a polished package when you are aiming for publication. If you treat editing like it's not actually part of the craft, the professionals you submit to are unlikely to see your work as a diamond in the rough. Competitive markets have too many authors submitting who took the time to polish their work and cut it out of the rough themselves, so there's a very good chance that if you throw a "diamond in the rough" onto their desks, they'll see nothing but a clod of dirt and throw it back at you.