They believe if an elect baby is aborted, the baby is somehow given faith and enters the kingdom of the elect. Thus if any elect did not hear the gospel, they too would be saved. So what then is left? Why preach the gospel - because that is what God commands, even though it does not alter the predestined outcome of every life.
Just so the readers might know:
Calvin, himself did believe in the horribile decretum, however it is a most lonely stand. For those who don't know, that is that even babies were sent to hell.
Spurgeon and others of Calvinistic thinking folks have reputed and spurned such declarations of Calvin.
Being Baptist, Spurgeon of course endorsed the time of one becoming aware of their sin (sometimes referred to as the age of accountability).
Now on to what Van posted:
Van, you present a true problem with the extreme Calvinists and that is why some of them actually teach there is no need for any outreach programs and evangelistic work. Of course on the far other side of the argument is the teaching of no literal hell and a teddy bear God. So, there is fault on both extremes.
Calvinists do not know who is and isn't part of the elect (other than their own personal salvation) and because they believe the giving of the Gospel is mixed with faith to salvation, evangelism is extremely important.
The typical Calvinist is not as concerned with how many are saved but with how many will hear the Gospel.