I’ve had the same response in the past, but I think it’s worth mentioning just for sake of discussion that there’s some justification for going against upstreams wishes, though I’m not specifically saying do or don’t.
Calibre specifically is a GPL3 application, and that’s a choice made by the developers themselves. It seems conflicting to me they would make it to be GPL3 whilst also basically encouraging people to revoke the rights they grant for it being GPL3. Regardless, it’s legally viable.
At a guess, they don’t want people making third party packages because bug reports could end up being sent back to upstream which are introduced by the third party packages. I think this is a valid excuse ethically, it’s understandable to ask people not to give you more work to do that they’re not responsible for. I think this is a strong arguement for respecting upstreams wishes, because I’ve seen it in action, it essentially adding cost to upstream unfairly, given they ask not to.
But it’s something that needs to be weighed against the current scenario, that third party packages do exist already, including in Ubuntu’s own repositories. The question then could be viewed as, would the Snap be better than the other options available, and if so, by having more people use the Snap does it decrease the amount of issues third party packages generate overall.
If the answer is yes, then honestly I’d say that despite the upstreams wishes, it’s still a good move overall for both users and the upstream to snap it. But if the answer is no, for example, if snap creates new categories of issues that innately unfixable or this might tarnish their brand or their bug tracker, I’d be inclined to hold off snapping it too.
I think basically it’s a nuanced decision that’s worth making on an per app basis, there’s some valid justification for respecting upstreams wishes and some valid justification to ignore it, and either option is valid depending on perspectives.
Just my 0.02$