Sceptics and debunkers will jump on any detail with which to undermine confidence in an impressive ufo case or abduction case. Amidst a shower of sceptical and debunking responses, the confidence of many people interested in a particular case is shaken. This experience repeated over years does shake general public confidence in the existence of a core reality expressed in ufo phenomena, except for those steeped in a broad range of the ufo research history. In Walton's case, the failure of lie detector tests is taken by some ufo research followers to constitute a fatal flaw; it shouldn't be given that we know lie detector tests are considered so unreliable that they are not yet accepted in courts of law.
In addition, I think it's understandable that people such as Walton who have come through a chaotic, terrifying, and only partially remembered experience and then repeatedly been doubted, challenged, put on the defensive, and called liars (in the media as well as in the streets, coffee shops, and pubs) would likely become so apprehensive about a lie detector test that something like a 'self-fulfilling prophecy' takes place. We're all social animals; what the people around us think of us and project onto us decenters us psychically, disables our confidence in what we know deeply to be true, and our insecurity is what shows up in the failed test..