The "value" of fallacious argumentation revisited

While rereading Robert Reymond's The Justification of Knowledge, I stumbled across the following quote by Clark who, using the cosmological argument as an augmentative example, argues the same point I did in a recent post; that is, that in the realm of evangelism and apologetics, invalid argumentation is only arbitrarily "valuable":

“If one wishes to use the cosmological argument without asserting its formal validity, there is a difficulty that requires explanation. The expression that the natural evidence for God’s existence is convincing for all practical purposes must be understood as simply a form of enthusiastic speech, for obviously it cannot be taken literally. There are many people, both Christian and unbelievers, to whom this argument is by no means convincing; nevertheless, the conversion of the unbelievers and even the enlightenment of the Christians would have to fall within the class of all practical purposes. If then it is not satisfactory for all practical purposes, can it be defended as satisfactory for some practical purposes? After all, it is convincing to those who use it. But this explanation is no better. People are frequently convinced by the flimsiest of evidence and the most glaring of fallacies. If it is justifiable to use an argument merely because it serves some practical purpose, would not evangelism be reduced to utter sophistry? Any evidence or any fallacy could be used, if only it were convincing to the person addressed. And this would remain the case even when the evangelist himself knew that his arguments were inherently unsound. The confusion arises from the unwillingness to see that an argument is either valid or fallacious. There is no third possibility. And in choosing arguments there is no substitute for valid logic.” (Contemporary Evangelical Thought, pgs. 149-150)