Pearls

Do not give that which is holy to the dogs; nor cast your pearls before swine, lest they trample them under their feet and turn again and tear you. (Mat 7:6)

Indeed, do not. For every sound Christian there are basics of faith that have always been true and indisputable. We take them for granted almost, believing that noone could possibly question them, ever. But when you stand before sect members, everything is possible, and there are no sacred issues of your faith.

How do you then talk to a cult member who denies the very essence of Christianity, i. e. Deity of Christ? And even after being presented with every possible Bible verse, with every possible Bible interpretation, the only shaky answer they give you is:
'Oh, all right, I might agree that Jesus is 'of God'... But he is not God.'
'Who is Jesus, then?', I ask, knowing the answer to come, but still wanting to chill down a bit.
All possible answers come, none of them logical, biblical, sound. All of them being the result of brain washing of a powerful cult, preying on ignorance and desire of belonging.

This is my warning to those who think that dealing with sects is a piece of cake. Well, it isn't. You may know your Bible well, you may be able to use it as a sword of Christ, but there is mostly one outcome - you scare the opponent, but you will not convince him.
Why is it so? Is the desire of belonging, the false support of a group so powerful, that even God's Word cannot penetrate through it? Or is it the fear of rejection by someone the person trusts and has invested a lot into? How strong are the bonds of deceit, planted by the leaders of a sect? Why do people agree to be mislead?
Good, decent people, once searching, now tired of looking, satisfied with the false doctrine, finding in it some strange and twisted comfort.
The answer is in The Bible. As always. Why do not they see it?

Beloved, believe not every spirit, but prove the spirits, whether they are of God; because many false prophets are gone out into the world. Hereby know ye the Spirit of God: every spirit that confesseth that Jesus Christ is come in the flesh is of God: and every spirit that confesseth not Jesus is not of God: and this is the spirit of the antichrist, whereof ye have heard that it cometh; and now it is in the world already. (1Jo 4:1-3)

For help and support in witnessing to JW's, go to K&K Ministries. It is one of many wonderful places where one can learn how to deal with the false teachings of sects.
Brooklyn.org.pl is a Polish site on the same topic.
Besked.se is a site in Swedish.