IIUC, the parent [1] is talking about 2 scenarios going on

1. If you're planning to commit arson you want to have encrypted radios to not get caught.

2. If you're planning a peaceful protest at a location somebody might commit arson you want an encrypted radio so you don't get unfairly punished.

I don't think anybody is arguing that (1) is desirable. They're arguing that the people involved with (2) shouldn't be punished for (1)'s crimes.

[1]: https://news.ycombinator.com/item?id=42833935