Mad Magazine (1, 2) says something like:
"March 17, 400-something: St. Patrick introduces Christianity to Ireland, thereby giving the natives something to fight about for the rest of their recorded history."
Actually March 17 was the date of his death. It's still a good quote. Apparently, it's also a good reason to wear green and drink pints of beer in Irish pubs all over the world.
"When the missionaries came to Africa they had the Bible and we had the land. They said "Let us pray." We closed our eyes. When we opened them we had the Bible and they had the land." Desmond Tutu