In my experience, the only people who are open to radicalization and aren't going to turn and run from a Marxist speaking about communism are people who are currently politically apathetic. When someone develops an interest in politics, they have a lot of questions that need to be answered.
This is why our rhetoric is so important and so valuable, we have to be the voices these people hear first when capitalism fails them. For me personally, my interest in politics began in my teenage years. Unfortunately, the rhetoric that found me first was fascist rhetoric, and it took years of deprogramming, reading literature, and having a Marxist family member be there to guide me to where I am now.
So, clearly it's possible to deprogram, but it's a personal choice someone has to make to want to be deprogrammed. Our efforts are better spent on those in our lives who have yet to develop their political identity.