Nobody is here to defend child pornography or terrorism. But even accepting that they exist, those are a drop in the literal ocean of use cases for encryption relative to the overwhelmingly legal and productive and often necessary uses.
> They should come up with a useful alternative
We have a useful alternative - criminal laws. Make the criminal penalty a strong enough deterrent and you'll stop everyone except the most craven malfeasors (and those people will find ways to continue to disseminate their materials irrespective of encryption status).
Rather than accuse privacy supporters of being "stubborn", you should come up with a legitimate argument why ordinary, law abiding people should have to sacrifice their autonomy in service of an effectively phantom boogeyman.