They subscribe to a belief that private speech should not be surveilled. I'm partial to their views. For all of human history, any two people could get together and privately talk. Talk about anything, including committing crimes. Now communication methods have changed but people still want to get together and talk about things, privately. Some of those things include crime, sure. The problem is it's not your freaking business what anyone is talking about privately. As soon as you open the door to surveillance "because crime", now you also have surveillance because you disagree with the government. And when it comes to internet surveillance, everything is preserved forever and also sold/leaked routinely, so you're really committing to leaking everyone's private life to anyone who is interested, forever. The internet is such an integral part of how most people communicate that "just don't say anything personal on the internet, ever" is not in any way reality.

I think this is not a line that can afford to be crossed. It is better for criminals and terrorists to be able to communicate privately than it is for no human anywhere ever to be able to communicate privately. It is not worth stripping the rights of billions of people to target a tiny minority of bad actors. And, given the trivial potential for authoritarian governments to misuse the power of absolute surveillance, I think the world we end up in would be much, much worse. Allowing nobody to privately communicate opposition to the government will lead to much worse outcomes than allowing nobody to privately communicate about crime, despite best intentions in short-term-thinking harm reduction. In addition to the criminal groups you mention it being wanted in Europe for, Telegram is also being prosecuted in Russia for harboring anti-Putin-regime activists! Such is the inherent nature of private communication.