The argument for violating privacy in communications is literally that it is being used as a mechanism for breaking the law.
I'd be interested in hearing a logically consistent argument for why bad guys hiding illegally gotten gains is a legitimate reason for opposing banking privacy, but bad guys using encrypted communication platforms for planning crimes isn't a legitimate reason to oppose communications privacy.
In both cares, the information would of course only be available to the government who will only ever use it for Legitimate Good(tm).
But by that logic it should be ok to monitor everything anyone does because if you do not, a person might be able do to something illegally under the cover of privacy.
I don't understand your use of "monitor" here. Banks by their very nature "monitor" your financial details, what else are they going to be doing?
Swiss banks will routinely refuse to honour legal requests for information from international law enforcement, e.g from 3rd world countries investigating their own corrupt politicians.
I think the critique is that the privacy is being used as a mechanism for breaking the law, by hiding illegally gotten gains.