They want people to think like that because they've built businesses that require it. Telegram stores the messages you send/receive unencrypted on their servers. That's not good, unless you've been trained to think that "privacy" is just about choosing the company, government, or legal jurisdiction that gets total access to your data.
Security professionals know that's not how we should think about security (never trust people!), because Durov is leaving a lot out: there aren't safe jurisdictions, servers get hacked, and centralized databases will get compromised. Logic, though, is probably no match for conspiracy theories.
1: https://www.washingtonpost.com/news/the-intersect/wp/2015/11...