The author of the article in CommonDreams.org may have fallen, however, for one of the old Thomas Paine chestnuts that still circulate far and wide with little or no historical support. In this case, it's the following quotation:
".... on April 14, 1775, the first anti-slavery society in the American colonies was formed in Philadelphia.
Thomas Paine was a founding member."
This story traces back, insofar as I have been able to ascertain, to Paine biographer Moncure Daniel Conway who presented it as fact without documentation in support his claim or attribution to his own source. Some years ago this writer spent a great deal of research time trying to trace down the facts surrounding the claim ... and came up 100% empty-handed. Extant primary sources -- at least the ones I have seen to date -- fail to mention Paine's name. Certainly the question can be said to remain open, but while it's tempting to believe that Paine would have if he could have, the fact remains that we do not know and there appears to be no good historical basis for the claim.