Why don't we encourage conversions
Conversion is a great way to swell our ranks and frankly the only way to ensure our demographic survival. Why should we always suffer as a tiny minority. Lets assume that we can convert 10 million people to Judaism. That would double the number of Jews in the world in the span of one generation.
Is this impossible? Not if we think Judaism is something worthwhile. Both Islam and Christianity obviously grew their ranks through conversion and not procreation.
Does this mean that we need to give up our principles? I don't think so. Even assume that we follow strictly Orthodox conversions to satisfy all factions of Judaism it is not at all impossible. You may not be very successful in Belgium, but what about South America or Africa or even the United States. There are plenty of people that are looking for a way to connect spiritually and Judaism can certainly provide as good a conduit as the other major religions.
So why the taboo?