Liberalism first became a powerful force in the Age of Enlightenment, rejecting several foundational assumptions that dominated most earlier theories of government, such as hereditary status, established religion, and absolute monarchy. The early liberal thinker John Locke, who is often credited for the creation of liberalism as a distinct philosophical tradition, employed the concept of natural rights and the social contract to argue that the rule of law should replace absolutism in government, that rulers were subject to the consent of the governed, and that private individuals had a fundamental right to life, liberty, and property.
John F. Kennedy defined liberal as "someone who looks ahead and not behind, someone who welcomes new ideas without rigid reactions...someone who cares about the welfare of the people".
So what's so bad about that? Liberalism brought us the New Deal which helped the nation recover from The Great Depression; it brought us the Civil Rights Movement; liberalism also the American Revolution... yes those things might be long past but where would we be today without the free thinkers that brought them about?