Rav Kook explained in Orot that the way to fight for ones ideology is not through showing the other person that he is wrong. If you show someone he is wrong, even if you are convincing, it is very unlikely that he will change his mind. The reason for that is simple. By showing him his ideal is wrong, you have showed him what mistake he has made, but you have not explained why he clings to this mistake, what spark of truth is found in this mistake in order for him to cling to it. By rejecting his ideal, you are rejecting his truth without trying to explain his truth. Therefore, he cannot accept your truth because your truth rejects the truth which is found within his ideal.
For example, there was once a very educated person who told Rav Cherki that even though he became more religious, he stayed communist. The reason is simple: the only movement that ever spoke to his ideals of social justice, was communism. And even if communism has been proven as false both on an economical and moral level, he could not let go of this ideal because it held a spark of truth that he could not find anywhere else. If he would leave communism, he would leave this truth. He did not find in the beit midrash anyone speaking of such social justice. The way to talk to such a person is not through Kiruv Rechokim - Showing him why you are right and he is wrong, showing him how communism is wrong. No! The way is through Kiruv Levavot - Learning from him where he is right, the importance of social justice, and then showing yourself how it fits perfectly within the structure of Authentic Judaism, understanding that maybe you have put too much emphasis in your own life on making people wear tfillin without putting any emphasis on social justice. Through this, not only may he possibly do tshouva, but you might also do Tshouva by being more in tune with the values of social justice expressed in Torah!
Let us not forget that we all want to do teshuva. Teshuva is not just for the secular. Therefore, an honest religious person should yearn to learn from every single person in order to better himself and get to the whole truth.
Real Kiruv - Kiruv Levavot - is one in which we are also brought closer to God through what we learn from the other. Through learning from his ideals, we also get closer to each other.
(To be continued ...)