The Wave is bad to the point of obsession. It's a natural thing for someone to lose themself in their work, but Ben Ross takes this idea to the extreme through the various ways he gets involved in what he's studying. For instance when he studied American Indians, "For months he was so wrapped up in Indians that he forgot about the rest of his life, On weekends he'd visit Indian reservations or spend hours looking for old books in dusty libraries." He even started bringing Indians home for dinner! And wearing deerskin moccasins". Another instance that shows Ben Ross' obsessive personality is when his wife, Christy taught him how to play bridge, not only did he become better than his wife, but he would also demand they play a game every night. It's for reasons like this that Ben Ross' personality is addictive to the point of obsessiveness, and it is for these reasons why when he gets involved in the Third Reich trouble would surely follow. And trouble was exactly what followed when Ben created the Wave, it started out as a simple enough classroom experiment, but soon evolved into a miniature version of the Third Reich.
Many, if not all of the problems in this novel stem from the fact that those who blindly follow others are willing to hurt, bully, and coerce other people into joining the crowd. The Wave started out peaceful enough when it was contained within Ben Ross' History class, but when the Wave spread outside the classroom and began to flood the halls of the school, various members took it upon themselves to bully other people into joining. Also the blind violence and hate that can pass over anyone's judgement comes into play with mob mentality because those that take part in the abuse do so because it gives them a sense of fitting in; this is also done to avoid punishment from others in the mob, just as the Nazis followed through with Hitler's "Final Plan" to the "Jewish Problem".
Bridging off mob mentality: fitting in is as important a theme as any considering a movement is nothing without people; for without people to carry the movement forward it becomes nothing more than an idea. The reason the Wave was met with such success is because it made people feel like they belonged, like they were becoming a part of something higher than themselves. Another important reason people were so eager to join the Wave was because of the fact that many of their friends were doing it, and they didn't want to be left out of such a huge fad.
They say that absolute power corrupts absolutely, which appears to be the case for Ben Ross. Aside from overall student enthusiasm, one huge reason as to why the Wave lasted as long as it did was because Ben Ross felt like he was being respected for the first time. He loved how eager his students were to learn his material, but mostly he was in love with the power that came with their respect. And according to Ben, "it's amazing how much more they like you when you make decisions for them".  It is through the Wave that Ben is enlarging his own ego while crushing his student's individuality to make them function like a single unit.
History repeats itself
An old saying has it that those who don't know history are doomed to repeat it, and this seems to very well be the case for those involved in the Wave. The students don't understand why the Nazis did what they did and some of them downright disregard the events ever having happened. And those who are aware that these events actually did happen doubt the possibility of something as horrific as the Holocaust ever happening again, though little did the students know; the Wave was beginning to turn into a mini Third Reich