You don't see a problem with them threatening even their non-Libra business lines with "additional scrutiny"? The letter directly threatens malicious investigation.
Interesting word choice there. I saw nothing malicious in the statement that moving forward would result in elevated regulatory pressure. That is a regulator's job. If Libra took off, but could not be monitored through the existing regulatory infrastructure, then those organizations must do more to make up the lost ground to meet their mandate.
So malice doesn't really come into it.
The financial system is regulated through high barrier entrance controls, and various levels of traffic pattern analysis through AML laws. Libra threatens to blow a hole in that for some period of time while the tools and processes are updated. Therefore... More scrutiny.
It isn't a conspiracy. It's just how things work in strictly regulated industries. Although usually, it isn't such a big deal that Congresspeople get directly involved through constituent outcry, and it is left to the Executive agencies to do the back and forth with the industry to ensure things go without a hitch.
It also should be obvious but something like Libra could easily affect other lines of business for a company and so those other things that don't necessarily deal directly with Libra would require monitoring as well. It's not a threat, it's just a fact of what (imo very warranted) enhanced regulatory attention risks.