I liked the reply you posted, I'd be happy for getting such feedback / replies. And I think your reply can be edited a little bit, to start in a little bit more positive tone,
by changing from this:
> There are many, many problems with the idea, ...
Nope. I think it's better to start with, This is interesting. then the questions. if you really see problems, state them. lead with engagement not criticism.
by changing from this:
> There are many, many problems with the idea, ...
to instead:
> I can see problems with the idea, ...