Its a fine line … by ignoring them, you can come off as "being afraid to debate them". Just look at the Tea Party and a lot of their their BS …
The Tea Party is a perfect example of what I'm talking about. They are a fringe movement, even among Republicans and they are viewed negatively by a majority of Americans. But it was because CNN and FOX gave them so much coverage initially, they inflated the commonality of the position and gave a fringe movement credibility, and as a tiny minority they were able to push Republican politics further right than they have ever been, which has now cost the American economy Billions of dollars, the Tea-Party led shutdown alone cost the economy 24 Billion dollars. If CNN and FOX had presented the story truthfully, the truth being that a couple thousand people, who had just had their taxed LOWERED, were being organized by Freedom-works (a Koch Brothers funded political organization) and needlessly protesting against non-existent tax increases, there wouldn't have been a tea-party, period, and according to most economists the GLOBAL economy would be better off.
All one has to do is look at Republican positions before and after the Tea Party to see how much promoting fringe concepts can change the course of events, to the detriment of a nation. They supported stimulus spending during recessions (was accepted as fact pre-tea people that stimulus spending promoted economic growth), infrastructure spending, individually mandated health insurance reforms and exchanges (a Republican plan)… the list goes on and on.
Giving Air-time to fringe concepts, particularly those concepts devoid of attachment to facts (like the tea-people and Young Earth Creationists), promotes them, often to the detriment of political discourse and the advancement of knowledge.
By ignoring fringe movements like Young Earth Creationists, you're taking away their soapbox and megaphone, reducing their credibility and putting their fringe ideology back into the minority of churches and Creationist 'museums' where they belongs.