An excellent blog post from Steve Sailer about why it is Liberals can never win an argument on facts, reason, and logic, and instead resort to tears and name calling.
Mostly, it's because they're all little crybaby, bed-wetting, thumb-sucking momma's boys who wear purty pink panties that have a tendency to get bunched every five minutes. It's the legacy of feminism and multi-culturalism that the once- Male Virtues of Free Thinking and Intellectual Acuity have been downgraded, and our political discourse has suffered greatly for it.
It's the primary reason why we got saddled with Nancy Pelosis, Hillary Clintons, Debbie Wasserman-Schultzes, and Barack Obamas, because to tell the indisputable truth about anything is to hurt someone's feelings, and therefore, make any salient point null-and-void in the minds of the truly brain dead.
This helps explain a lot of what has been happening in American society and politics for the last 30 years, at least.