penal substitution

This post and its comments have been reproduced on the commentary subsite . Discussion should be continued there. 

The doctrine of ‘penal substitutionary atonement’ remains a major bone of contention between the yapping, excitable Jack Russell of the emerging church and the snarling pit bull of reformed theology. There may be some dispute over the choice of dogs, but the seriousness and persistence of the disagreements is apparent from, for example, the 9Marks Forum and this paragraph from an essay by Albert Mohler in which he quotes from D.A. Carson’s Becoming Conversant with the Emerging Church:

Given the fact that both McLaren and Chalke deny the substitutionary nature of the atonement – indeed, rejecting virtually any notion of penal substitution – Carson sees the ghost of a discredited theological liberalism. ‘I have to say, as kindly but as forcefully as I can, that to my mind, if words mean anything, both McLaren and Chalke have largely abandoned the Gospel,’ Carson laments. ‘Perhaps their rhetoric and enthusiasm have led them astray and they will prove willing to reconsider the published judgments on these matters and embrace biblical truth more holistically than they have been doing in their most recent works. But if not, I cannot see how their own words constitute anything less than a drift toward abandoning the Gospel itself.’

With the EA having recently declared that penal substitution is central to a correct understanding of the atonement, does this mean that anyone who challenges the concept is, by definition, no longer an Evangelical?

Or does it mean that the EA has simply swerved to the right and is no longer a representative group for Evangelicals?