There's something simpler. Leftists want power, really want it.
That means they have to hate and attack ANYTHING in their way. No matter how big or small. Attack it and kill it.
Here's a partial list of things in their way: family, religion, good schools, patriotism, capitalism, guns, knowledge, reading, arithmetic, history, independent thinking, manliness, bravery, traditional marriage...basically, everything that the Founding Fathers would have thought more or less ordinary.