It's a concern, yes, but also useful functionality. Two examples from other software: OpenSSH AFAIR logs every keystroke when in high enough log levels (and accordingly warns that using DEBUG1-DEBUG3 log levels violates user privacy). Postfix will log user passwords if asked to do so.

Having multiple levels of DEBUG like OpenSSH or extra options like postfix probably is a good idea, and as is printing an explicit warning if started with such log levels.