Stereotypes are very easy to buy into. They are promulgated mostly by bad leaders who value the goal of gaining and holding political power more than they value the idea of using political power to solve real-world problems. It's far easier to gain and hold political power by misrepresenting a given group of people as a dangerous enemy threat that only your political party can defend society against, than it is to gain and hold power solely on the merits of your own ideas and policies. Solving problems is very hard. Creating problems to scare people into following you is very easy.

We are all guilty of believing untrue negative stereotypes. We can fight against stereotypes by refusing to believe the ones we are told about others, while patiently working to dispel stereotypes about ourselves or others, with the understanding that those who hold negative stereotypes are victims of bad education and socialization - and that each of us is equally susceptible to the false sense of moral and intellectual superiority that comes from using the worst examples of a group to create stereotypes.

Most conservatives are hostile towards the left because they hate being unfairly stereotyped just as much as any other group of people does. When we get beyond the conflict over who gets to be in charge of public policy, the vast majority of people on all sides can agree in principle that we do our best work as a society when the progressive zeal for perfection through change is moderated and complemented by conservative prudence and practicality. When that happens, we more effectively solve the problems we are trying to solve, while avoiding the creation of more and larger problems as a result of the unintended consequences of poorly considered changes.