Let's not forget: privacy is not a sign of wrongdoing.

Some friends wanted to make a podcast, and asked me to join. I agreed under the condition that I could use a real-time voice changer, because I didn't want my real voice publicly on the internet. That's one legitimate use case. Maybe OP is calling a support number, which often monitor and record your calls. OP could also just be calling a friend, you never know who could be listening in.

In any case, voice changers are just software. It's not creepy unless you know for sure it's being used for something creepy. Anything can be used for good or bad.