Yeah, people did that in 2012 too....didn't work out quite so well.
Dismissing polls is foolish. Even if they are wrong it is better to operate as if our candidate is the underdog.
Even if losing, Trump is within striking distance. If he turns in a couple solid debate performances it could change the entire dynamics of the race. Right near the end of a campaign there is sometimes a surge of movement one way or the other - a couple debate wins could push a lot of support to Trump.