It did somewhat help my self-esteem by kicking it into the hole over which it was leaning so precariously, but they're better than whatever the average stone would produce in its lifetime, that much must be said. Well, I've now decided not to upload most of them at all, maybe one or two if I feel like it.
Thank you all for the responses. So what I think I should do, based on what you're all basically saying, is I should rather not upload the entire piece if I plan to have it published later, instead I should upload a portion of a story, a shortened version maybe. Or I could upload an entire story that I believe reflects my abilities, at the risk that I may not be able to publish it later, but then I could apply the criticism of that story to my others.
As far as I heard your submissions here are time-stamped, so in case someone plagiarizes your work you can always prove that you have uploaded it first. Maybe don't upload *all* your work, but only a selection of your short stories. Or only excerpts in case of a novel. So people who like your work still will have a reason to buy it (I think this is the main issues publishers are having with stories already published in the web: why pay for something, when you can have it for free?) The constructive criticism you hopefully will get you still can apply to the parts you don't show here.
Like basically everyone above has said, whatever you upload you still hold full copyright over. However, also like others were saying, publishers don't like to publish works that are already published most of the time (there are a select few that will). They want first-publishing rights. When you upload work to dA, it's considered "publishing" it and therefore, since it's available "free" to the internet, publishers won't publish it.
However, you can make it so that your work is seen ONLY on dA (which is good if you don't want people being able to read your work if they don't have an account), and you can always take your work down after you get the feedback you need. DO remember, though, that everything you upload keeps a record on the internet, so it will take a long time to (if you're lucky) scrub the presence of your work clean. (A friend of mine is a comic writer here and took down the last few pages when he was looking to pitch it, and even after it was removed, the story was still able to be found via google).
As far as I'm aware, anything you upload to DeviantART you still retain copyright over. However, personally I don't upload anything online that I might one day want to publish anywhere, because I've heard it seriously damages the chances of it being published, so you might want to bear that in mind when choosing what to put here