Search engines do not (and cannot) distinguish between 'dupe' and 'legit' - they have no way to know which you consider to be legit.
Me too; if you submitted it (as opposed to 'it was nicked'), it's as legitimate as the one on your own site, isn't it?
There is such a thing as a quality article farm - but they are few and far between; in almost every case, the article on your own site will do you more good than farming it out.
Many link farms obfuscate links.
Few link farms have any page rank to share.
Very few link farms actually refer many human beings.
Plus the duplicate content issues.
Whereas the article on your own site:
Gives you credit
increases your page ranking, as your site becomes more substantial
earns organic links
is something to be proud of.
Article farms are 2005 going on 2006 as an seo 'trick' - then people realised that they were 'assuming' a value in article farms that only about three of them possess.
They arose just as link farms were dying; I guess people still had the agricultural theme.