Gatland said: "We just feel like the destiny of the result was taken out of our hands with the red card.
"He's lifted him, that's a yellow card, but he's not driven him into the ground."
Wales face New Zealand or Australia in Friday's third-place play-off.
Gatland remained proud of his side's efforts in a game in which scrum-half Mike Phillips scored the only try.
The New Zealander added: "Does that mean every time there's a tackle where you lift someone off the ground it's a red card?
"Why spoil the semi-final with a red card? He's not a dirty player. I'm just gutted.
"We were down to 14 but we showed great character and I'm proud of our efforts.
"But we can't go to just one tournament and do well, we have got to kick on from here.
"I feel let down, I thought this team were good enough to go on and take the final but it was not to be.
"We just feel that ultimately the result wasn't in our control."
Wales centre Jamie Roberts,who joined the scrum at times in flanker Warburton's absence, said: "To play like we did with 14 men for 70 minutes, we can take a lot of pride in that performance, we hope everyone back home is proud of us but it is heartbreaking.
"Obviously with 14 men you have to close the game up a bit - the stint with me in the scrum was quite interesting.
"We went to a kick-chase game which paid dividends, we clawed our way back territorially and had a couple of opportunities to win the game.
"It's fine lines at this level but hopefully we've done everyone proud.
"We'll train hard this week, we won't throw it all away now, and try to win next week."
Prop Gethin Jenkins said: "It was always going to be tough with the sending-off but we gave it our all right to the end. It's just disappointing.
"It changed the game a bit, we had to play a different style but fair play to the French, they held us out.
"We'll work on what went wrong, we've got a young side for the future."
"With 14 men you have to close the game up a bit, we went for a kick-chasegame and it paid dividends really.
"We had a couple of opportunities to win the game and unfortunately Stephen hit the post and Leigh was half a metre short with a kick from the halfway line.
"We train a lot with 14 men, we defended for our lives out there and it just wasn't to be."
Wing Shane Williams said: "There's no bitterness, the side who played the best today won.
"We knew the France team turning up today would be a good France team - Parra at 10 had a great game, he bossed things. We wish them all the best in the final.
"We're absolutely devastated, we worked hard getting through the group and it was a great performance last week."