Secularfrummy, I think that you should find out more of the story before u go judging. Listen to some of his recent shiurim, and you will see that he says that he was speaking in Boro park to a group of woman who never listens to English music, and yes, listening to it at Zumba might make them want to listen to it at other times as well.
The same Rabbi Wallerstein that gave that speech that u heard about how you shouldn’t do Zumba (which btw only started at the 38th minute of his speech – and let me guess that you only heard that part and not the whole beginning) hired a DJ to play English music for his students from his high school on New Years from 12-3 am so that they shouldn’t be in other places.
So for the crowd that he was speaking to, it was wrong for then to go to Zumba, and for his high school, it was the right thing for them to be doing. He was only speaking to the crowd that he was standing in front of. I think that a Rav that gives advice to people based on the individual is much better then one that gives the same advice to everyone, regardless of the situation.