The historical St. Patrick was, it would appear, born AD 357 as Maewyn Succat in Britain. According to Roman Church sources Succat was a citizen of the Roman Empire and lived on the coast of the region now known as Wales. It is alleged that slave traders from Ireland captured Succat and transported him back to Ireland and bonded him into slavery. Succat was a pagan, until during his slavery in Ireland he became a Christian. He then started hearing voices that led him to escape slavery and return to his homeland of Britannia. On his return, Succat joined the ranks of the Catholic Church, until becoming a bishop. It was as a bishop he returned to Ireland to convert the pagans to Christianity.
It was around this period that the Roman Empire adopted Christianity as there official religion. During this period, the Catholic Church, the self appointed administrators of Christianity were still heavily immersed in the slave trade despite this contradicting Christian doctrine. The so called pagan people of Ireland were not known widely for there use of slaves. In fact, a system of clans maintained the social order, largely based on libertarian values. If the pagans did keep slaves, kidnapping them from the most powerful empire in the world would be the most unlikely notion imaginable.
The track record of early Christianity would also suggest that Succat having climbed the ranks of the Roman Church, led a military campaign of extermination of all heretical pagans. This essentially became a genocidal campaign, with the destruction of the ancient religious culture of Ireland as the primary objective. Many sacred pagan sites were destroyed, covered, re-branded with Catholic relics, churches and monuments etc... The Holiday itself, like most Christian holidays is set around the same time as an older Pagan holiday. Again the tactic of covering over an older sacred thing with the new conquering faith.
So when celebrating this day, think about what your really celebrating, the genocide and destruction of a culture much older than Christianity.