He had been expecting his team to still be in contention for the title, if not the Grand Slam, going into their final game of the tournament.
But defeat on the opening weekend by England at Twickenham, and then more painfully by Ireland in Dublin three weeks ago, meant those hopes were shattered.
And Laporte admitted he has not yet recovered from that psychological blow.
"I am still frustrated by our match in Ireland," he said. "If we'd beaten them (Ireland) we would look at Sunday's match (between Ireland and England) with the great expectation of retaining our title.
"But instead we will be watching television with friends, without being worried at all.
"This defeat cost us a lot and is definitely the biggest regret of our 2003 campaign.
"Winning against England is always difficult, even nations from the southern hemisphere have problems beating them, but Ireland were beatable.
"We lost the match on penalties, on points we gave them, and that is why we lost the title in the end."
This feeling of frustration was also shared by France captain Fabien Pelous.
"I also have only one regret in this year's tournament and this is Ireland," he said.
"We could have won that match and we did not do it. This is frustrating because by now we would still be in the race for the title."