It's not a cop-out.
It's a cop-out if you say "laziness" as if it explains anything. That's like the police finding a crime scene and concluding that the gun killed the man, and then packing up their things and going home.
We need to figure out why people are lazy and check if we can address it. Maybe we're making it too difficult?
Here's an example: Backups. Even I didn't have a good backup regime until Apple came up with Time Machine. It's just too much stupid work. But someone sat his ass down and asked the right question. And that's not "why are these fuckers so fucking lazy?", but "how can we make it easier for the users?".
they usually see as *an obstacle* to fun
That exactly is the point. If people see our work as an obstacle - maybe every once in a while we should climb down from our high horse and admit that they could be right?
Threema is only $1 more than WhatsApp. Pop quiz: how many people buy these over the insecure alternatives? Now you know how much the users care.
Messaging apps are driven purely by networks. If all your friends switched to Threema, you'd do it too. If nobody does it, you're unlikely to be the first. Security doesn't matter enough to lose contact with all your friends.