The 45-year-old actor stars as a suicidal man who has travelled to Japan to kill himself in the film.
Heckles and boos were heard at Friday's press screening, but McConaughey said, "People have as much right to boo as to ovate."
The film is directed by Gus Van Sant, whose film "Elephant" won the coveted Palme d'Or at Cannes in 2003.
Reviews for the film, which also stars Naomi Watts and Ken Watanabe, have also been fairly negative, with the Guardian's one-star review calling it "a fantastically annoying and dishonest tear-jerker".
Referring to the 2003 festival, he continued, "There was apparently some kind of fight after the Elephant screening, like fisticuffs over whether it was good or bad, which I thought was interesting."
The new film is also in competition for this year's top prize which will be announced on May 24.