Excellent post. Throughout this country's history, both liberals and conservatives have had worthwhile programs/policies to promote, and both, no matter how well intentioned, can have a tendency to go too far. This country has worked best when there has been a principled and respectful mix of both political philosophies, when the genuine welfare of the people and country are put ahead of party and self-interest. It is up to us as voters/citizens to reject extreme, negative partisanship of any sort, even when (maybe particularly when) it promotes a policy or candidate we tend to support. 
The only way negative, partisan political behavior is going to change is when we stop supporting/electing extreme, partisan politicians.  If we keep buying it. they have no incentive to change, and they will keep selling it. We need to raise the bar for all of our elected representatives, regardless of party or political philosophy.