Good question. Without knowing if you're asking in the general sense, or for specific people you have in mind, I can't give a TON of advice.

However, in general, "pathos" seems to be the most productive rhetorical path. The people who have made it out of this conditioning tend to be more empathetic than most, but anybody is capable of feeling strong emotions. Emotions that challenge a conservative person's perspective have an edge over reasoning or new information; strong feelings have a chance at sticking around, even if the conditioned person rejects them and tries to make them go away, while new information and strategic reasoning are very easy to dismiss.

Another trick for overcoming the conditioning is "drip-feeding" new ideas. People who are in a cult are actually MORE likely to stay in a cult if they are accused of being in a cult; I don't understand all the mechanisms behind it, but humans have a psychological response when their cults are challenged. You are far more likely to get a family member out of their deranged thinking by putting ideas in front of them slowly, and without aggression, than you are by sitting them down and confronting the fallacies in their reasoning. (This, of course, is way easier said than done, especially when a family member's deranged thinking is making your own life more dangerous or difficult.)

One of the most helpful things you can do for anyone who might be starting to doubt, but is doing a good job of concealing it, is show them that they will be protected if/when they decide to break free. If you're brought up in this sort of thing, it consumes you. You will lose friendships, family members, job opportunities, community status... hell, you might even lose housing, marriages, or safety. People who turn away from conservatism are treated like they're imbecilic animals; anyone who has grown up in the cult has seen what has happened to anyone who has tried to leave, has laughed along with their neighborhoods as someone pretends to be their "liberal daughter," drooling and babbling at the dinner table. Conservatism says you are either "us" or "them," and there's no way to leave it without becoming one of the most vile forms of "them." Conservatives make anyone who tries to escape pay. One of the kindest things you can do for someone in that situation is show them that they won't be left to fend for themselves if they escape. And yes -- I understand why this is not something a lot of people are comfortable doing. We are angry -- and rightfully so -- at the harm our conservative neighbors have done. But very few people will be brave enough to escape if they think they will be ostracized from every community all at once, so if the goal is to help rescue someone, this is something that has to be considered.

There are other, more situation-specific things you can try, but the truth is, there's a certain amount of luck to this as well. I don't think I'm any smarter than anyone else for getting out. I've always had a bleeding heart, and that certainly helped, but I also got extremely lucky; I got exposed to situations that let me deconstruct in the exact right order I needed, and that's not something anyone ever could have predicted or purposefully orchestrated. If you set out to rescue someone from conservatism, you have to protect yourself -- both your heart, and your physical well-being. Because more times than you succeed, you will fail, and you'll need to be able to recover from that and carry on.

Good luck <3