I don't believe the Virgin Birth is a "fundamental of the faith." Nonsense. It is not mentioned anywhere in the New Testament except for Matthew and Luke. [There are hints in Mark and John that the rumor that Jesus was a bastard was widespread.]Paul does not seem to have heard of it and, in the First Century, it was probably possible to be converted, live a Christian life, and die without ever hearing about, never mind believing in, the Virgin Birth. It is not necessary to believe in the Virgin Birth in order to believe in the Incarnation or Christ's pre-existence. John's Gospel and some hymns in Paul's letters indicate Christ's pre-existence without ever mentioning virgin birth. We get our very WORD "incarnation" from the prologue to John's Gospel without ever a mention of the Virgin Birth. Although some later theologians say the Virgin Birth guarantees Jesus' sinlessness, the New Testament never makes that connection--and doesn't promote a belief in the biological transmission of sin.
But, as a matter of fact, that is not MY view: I believe the virgin birth to be literal, historical fact. Because I believe the Resurrection is literal, historical, fact, I believe in a God whose relation to the world allows for miracles. So, nothing in my worldview prevents belief in the Virgin Birth. A God that created this cosmos (yes, using evolutionary and other natural processes, but STILL) and can raise the dead would have no trouble with a pathenogenetic conception in a species (Homo sapiens) where that is usually impossible.
Be sure to read the whole post, which is an excellent examination of the doctrinal implications of disbelief in the Virgin Birth [nota bene: I do not necessarily agree with Michael. I simply suggest that you read him.].
I do not think that there would be any causal relationship between professed disbelief in the Virgin Birth and reprobation. But I do think that disbelief in the Virgin Birth would be symptomatic of serious theological error. What possible reason would a Christian have for disbelief in the Virgin Birth? I cannot see any reason to proclaim the Gospel writers liars. If they fabricated the Virgin Birth, did they also fabricate the Sermon on the Mount?
The burden of argument lies on the laps of those Christians who declare that there was no Virgin Birth. On what basis do they declare the Biblical account false?