Some people object that the doctrine of original sin is unjust, for it holds other people responsible for Adam's (and Eve's) sin to the extent that they're condemned to hell for something they themselves didn't do. In particular, the objectors say, infants who die are condemned to hell as a result, even though they have not yet consciously sinned.
This version of the doctrine is not held by all evangelical Christians and is not an essential belief of Christianity. Many Calvinists believe that people deserve hell in part because of original sin, but many also believe that infants who die are among the elect and are therefore saved by God's grace (see Infant Salvation by Loraine Boettner). Other Christians, including myself, believe that we suffer the effects of Adam's sin - we are born with a sinful nature and will experience physical death - but we're not individually condemned to hell directly because of Adam's sin, for, "The soul who sins is the one who will die. The son will not share the guilt of the father, nor will the father share the guilt of the son" (Ezek 18:20).
Other responses (offsite)
The following article defends the view that we are in fact held guilty for Adam and Eve's sin: