Implementing end to end encryption in these messaging apps won't make any of these issues worse. The criminals this will supposedly help already have easy and convenient ways to do the same thing. The government has not caught anyone of any importance this way, so encryption of Facebook messages won't hinder any real investigation methods.

This won't increase the number of people affected or reduce the number caught. The only thing encryption can do in this case is make it more difficult for the government or foreign governments to read personal messages.

Not implementing encryption here can only help people violate people's privacy, it cannot help the government do its job.