If I left, I could go anywhere, really. Apply for PhD-positions around Germany or Europe. This conference thing is really bugging me. Specially because we don't have any contact to other researchers. And I don't see anyone of the students take any of the classes provided by the graduate school...
I've heard of poisonous grad school programs. I certainly would say to keep your eyes open and be aware of the situation as it progresses. I want to ask if this guy who's against you guys going to conferences appears to be leading any sort of cult of personality at the school. I don't think it's conducive to a good education to close off from others in your field - in fact, the opposite, really. He seems like he might be a bit egotistical (keeping his techniques to himself so others can't do as well) and wants your unswerving attention (afraid others will 'steal' away 'his' students/assistants/what-have-you). By keeping you from conferences, etc, he's also potentially preventing you from developing a name and reputation for yourself which you could do via networking, presentations, etc, at such venues. He is establishing himself as your only/main educational resource, and denying you the ability to pursue others.