Kevin points out that the other side lies, extensively, even when actual numbers are easy to come by and their lies are easily exposed.
He asks why do they do that. That is actually an easy question to answer.
As I have demonstrated before they are incapable of determining truth from falsity. They cannot distinguish their fantasy world from reality. This is part of the reason they can be so convincing with their lies. They actually believe them. The other reason they can be very convincing is that many of their audience want to believe them. They want to believe there are solutions as simple as congress flipping a switch and making the Boogie Monster under the bed go away.
They are frequently pathetic creatures for whom the light switch on the wall is, in a very real sense, magical. They have no concept of how things actually work. How else do you explain their belief that some collection of people could write down set of rules on a piece of paper and evil people, who fail to obey existing rules against violence crime, will suddenly obey still another rule to turn in or destroy their tools which enable them to pursue their chosen evil ways?
Of course do not underestimate our opponents. As Sean likes to point out, not all of them are so simple minded.