England added an arguably undeserved hint of respectability to the scoreline as they ran in late tries through Ben Youngs and Jonny May following Bundee Aki's dismissal just past the hour mark.
Sexton believes that sort of indiscipline had hampered Ireland throughout the tournament, and called for it to be eradicated.
He added: "We still felt we should have stopped the try - a missed tackle - but we showed great guts throughout the tournament.
"Sometimes when you don't take your chances, your performances are made out to be worse than they actually are.
"The first game, we go down to 14, and indiscipline is still an issue at times. And against France, small margins, all these games.
"Both of these teams could have been going for a championship today or a Grand Slam so they are the margins we have to make up next time we come together."
England put their points on the board through two Owen Farrell penalties - the second of which brought up his 500th Six Nations point - early in the first half and that late flurry of tries.
That left flanker Tom Curry rueing a failure to compete with Ireland in the "middle section" of the game.
"I'm obviously very disappointed. It's pretty gutting," he said.
"We knew it was going to be a really physical encounter. The past three times we have played them it has been all about physicality and today was no different.
"A bit of discipline cost us here and there. In the last 20 we showed a bit more of a glimpse of what we're about.
"It was that middle section where we need to back it up and we probably didn't do that today."
