No, of course no one is saying to throw out concordances but rather that untrained lay people need to know the limitations and dangers of using concordances and lexicons. Such an argument completely ignores the difficulties that often arise in biblical interpretation, particularly with such an obscure and difficult topic.
Read D. A. Carson's Exegetical Fallacies, or just listen to the podcast Principles for Biblical Interpretation by Dr. James Voelz, available in iTunesU for Concordia Seminary. Both state the danger of going to the root of a word since, as Sparrowhawke has correctly pointed out, the actual meaning between a word and its root can be quite different.
So, no, this very much isn't grasping at straws but rather trying to be faithful to the text without making assumptions.
Of course he isn't. Be careful in quoting Scripture as though you have said something meaningful. This much abused passage is often used when one has no response except to simply disagree, presuming that it is the opposing view(s) that is confused, implying they are following the flesh or demons, instead of acknowledging the possibility of one's own lack of understanding.
I have pointed out some other problems with the fallen angels had sex with female women theory, but as far as I have seen, they have gone unaddressed.