Bitcoin and altcoins' prices are falling down because of some people who panic sell their coins maybe because of some fake news spreading about crypto currencies. There are some people who want to destroy crypto currencies that's why they are doing it, maybe because they see the success of crypto currency and they don't like it.
There are a lot of different people but I don't believe that several people can destroy such a large and powerful crypto currency system that already exists. The reason I think is that the same people themselves want to go into crypto-currencies and want to do it at a good price, for this they lower the prices of tokens with bad news.