Mills I think that only in extreme cases ,maybe conversion should be allowed. Even dissuading is not enough, and only the strictest of the strictest Rabbis should be consulted (better the Sefaradi Beit din), definitly not someone who is in the wrong path completly (reform, conservative, etc.) and also not someone who has conversions relativly often (for example Habad).
*- mentioning Habad isn't becuase of the latest talk (about messianism) but that it is known that they are converting more people, and quicker then really allowed. (also some of those people then dropp the mitzvot, etc. and concider their children to be Jewish, where its a BIGGG problem because they are probably not). Sorry to say that their are a number of these "Jewish" children that are born, and their is at least 1 person on this forum who is in that situation, and it is a very serious, and dangerous matter.