Giving this some thought, I have to wonder: why is picking socially unsanctioned, but to reach over and give your arm a good scratch is not? I'll grant you that the flakes of skin that precipitate from the act of a scratch are not gooey as your typical nose nugget, but the fact remains that one is extricating from oneself dead cells freed by one's finger nails as a result of both acts.
I suppose there is also the size of the goober - with your common-or-garden boogie, there is a noticable chuck; whereas with your standard scratch, you're typically dealing with a microscopic dust. Nonetheless, each should be - to the thinking man - equally icky... or not. Choose your medicine, right?