I see the stances as very different. Parler is a social media site
dedicated to extremism. While I believe in their 1st amendment right to exist (not all speech is protected though) I do not like this group. On the other hand I see companies like Signal and CloudFlare as being neutral. They have taken a position that they choose not to be the arbiters of right and wrong. These companies also aren't
dedicated to extremism. I believe that being able to speak freely and make mistakes is an essential part of democracy. A privacy preserving platform protects this idea. If the service is
dedicated to the public (aka neutral) then I think this is the right move. Extremists will (and have) congregate on Signal (as they do on WA, Telegram, Twitter, 4Chan, Facebook, etc). I see encryption orthogonal to the issue of extremism. This may make it a bit harder for security to monitor these groups (no dragnets), but if they are mass groups it won't be hard to infiltrate anyways. If a member of the public can get in then why can't someone from the CIA/NSA? It might as well be in clear text. If they can't infiltrate these groups then we have much bigger problems and everyone has been overestimating the power of these organizations for decades.
So to sum up. I highly value privacy and security (especially as we're adding more to the internet. The danger is increasing). But I'm against extremism. It is a numbers game that more public members will gain value from privacy than the dozens of terrorists who will. But it is a different situation if someone creates a space dedicated to extremism.
(I do think this is a very reasonable question to ask though)
Edit: I wouldn't say that Signal will be completely unmoderated. Groups still have admins. But you're right that Signal won't be able to moderate. But this isn't that different from any federated platform.