oh the app is probably secure and might not have any backdoors. It's just like TOR being developed by DARPA. If you have an anonymous network but it's only used by the CIA/NSA, every other country will be like "oh look, it's CIA traffic again." But if you allow ever scammer/pedo/normal person/malicious actor on it, now it becomes impossible to differentiate what's a person vs government.
Signal is likely serving a similar purpose; and is promoted by three letter agencies to particular groups the US/EU/GB want to have uprisings in a given nation.