Well of you provide a service and it's knowingly used by criminals and you just implement features to benefit the criminal activity but make no effort to curb it. Yes, your an accomplice.
If the road worker built features that specifically provided an oversized benefit to the bank robbing community in general, you’d definitely investigate the worker or construction company
To get the analogy straight, they would definitely arrest the CEO of the roadworks company if the road was letting robbers through but hindering law enforcement and the CEO was refusing to make the changes legally asked of them to mitigate the problem, yes.
No it doesn't. If you set up PGP or SSL you'll be able to encrypt things and might even misuse this capability for crime, but you won't have installed a platform where crime is openly advertised.
I like Telegram, a lot, but if you're ignoring the fact that large parts of it openly function as a mall for criminal services (and it's 100x easier to find that stuff than via Tor, for example) you're not being honest with yourself. A lot of people here are just reflexively assuming its mean cops vs encryption because that's an issue tehy personally care about, and ignoring any other context.