Considering that Soundcloud gives uploaders the option to allow downloads, it's a pretty gross violation of the artists' intent to download tracks that aren't already explicitly downloadable. Many artists even offer an alternative download location in the track description for cases where Soundcloud's limit is exceeded. And, as zmitri has pointed out, it is perhaps of greater concern that tools like this make it harder for entities like Soundcloud to justify their existence to stingy music rights holders. I'm not saying you're the reason we get things like SOPA, but this is the kind of thing that allows the grinches at the RIAA to feel justified in asking for sweeping changes to the internet we know and love.
So, nice little piece of work you've done here, but as a reformed music pirate trying to stay clean, I'm going to have to stay away.
tl;dr - This is why we can't have nice things.