Is Messenger really an antipattern?

Question

Java

As far as I know it is possible to use RxJava or equivalent for C# to avoid using various MOM(Message Oriented Middleware) JMS and others as often as possible.
1. The question is why are various implementations of Messenger - called an anti-pattern and why should you avoid using it?
2. When is the use of this pattern justified?

Answer 1

Something I do not see any connection between RxJava and JMS. This is a comparison of traffic rules with gearbox standards.
RxJava - about events within the application.
JMS is about events between applications (maybe even in different languages ​​and platforms).