Liberals don‘t understand the importance of revolution, the cost of revolution, how it is misguided to complain about what necessarily happens in revolutions and why reasoning must reject and move past that of the established status quo because liberals are not taught the importance of their own revolution. You may learn about the events that have happened, but you are not philosophically educated about revolutions in themselves and their necessity in moving past a system that is inherently bad and whose rulers and those privileged will fight tooth and nail to keep it, at the cost of everyone else living in misery.
I suggest that if you want to convert liberals to socialism then educate them about the liberal revolution. Make them grasp the necessity and good of a revolution regarding something they wouldn‘t possibly disagree with. Additionally, you could then translate this to our times and make analogies of the current ruling class acting like kings and everyone else having to live like a serf.