How do we prevent this type of propaganda attack or invasion of privacy?
Technology alone isn't enough to stop those. While there are ways to protect your privacy which mentioned here, some people don't know how to use it and limiting which service you could use.
1. It is technically possible to hide things. Monero can do this, their features can be implemented by Bitcoin if needed.
While Monero features could be implemented into Bitcoin, it's very unlikely it'll happen due to various reasons. I'd encourage adaption of existing feature such as PayJoin on wallet and payment processor.