It motivates an opposing partisan for each of ones own. The Dems huge advantage in registration, generic ballots and overall make Republicans lucky if it fares even that well. Remember, low general turnout is a big part of their game plan, because they know that, all else being equal, Republicans are more likely to vote come or Hell or high water, out of patriotic duty, than decide both candidates suck and it is too cold/wet to bother. Look at Moderate Mitt running from the "severely conservative" candidate he called himself during the GOP primaries.

General elections are about the middle, especially for Republicans; appeals to the base usually lose more than they gain. Both candidates being so uninspiring this is likely to be a low turnout election somewhat mitigates that, but the only reason it is even close is the occasional/first time voters who turned in droves to elect Obama are staying home. Changing that dynamic would be a disaster for Republicans, and any candidate smart enough to hold office knows politics well enough to realize that.

Ultimately, it comes down to the same old thing though: Whether they are insincerely pandering to their base, completely uninformed about issues on which they volunteer to speak anyway, or naïve enough to walk face first into a trap, is any of those a quality we seek in federal lawmakers? Personally, I think they mean what they say and say what they mean, because they have no reason to volunteer controversial policy positions they do not hold (and every reason not to do so.) At least Akin and Co. are honest about it, and I can respect that a lot more than Romneys duplicity even if I disagree with their positions and know the "facts" they believe are false.