Why do people need a kick to exit the dream they are in in Inception?

Answer 1

because its like in real life. if you feel like your falling in a dream, you wake up instantly. In Inception, they are under a strong sedative, and so killing themselves in the dream would only send them to limbo, ( another section of dreaming in which you could have to stay there for years due to the time differences between dream stages) and so the only way to wake out of a stage / dream is to have a kick (give yourself the feeling of falling). in the film, it is your body that must fall, not your semi conscious projection in the stage of which you wish to awake. for example, at the beginning of the film, Cobb is in a dream state within a dream. that's 2 stages. to wake from stage 1, his asleep body had to be tipped into the bath to give the kick required to awake in stage 2. then the dreamer died when the music played to indicate that the sedative had worn off and it was time for another kick. in this case, the dreamer was allowed to die within the dream because he wasn't in a dream within a dream. so the kick is required to wake you up basically into a previous stage of dreaming.

hope this helped!