It's a rather complex issue -- not just how do delineate "libraries" as opposed to "derived works" -- but also how much is needed in the "main product" for it to be useful. Architecturally it might make sense to have the "program" or "service" be a thin wrapper around several libraries -- but if only the program is AGPL, and the libraries are LGPL -- how do we make sure the end user is free to maintain the software if needed?
The main thing with the GNU line of reasoning, is user rights. If viewed from the perspective as "just" a developer, many of the licenses look restrictive -- because it limits the developers power over end users.
I think we all end up with more freedom as a result of that -- not everyone agrees.
As for mixing -- I'm not sure how the "open source" exceptions in the license are supposed to affect that -- my cursory reading seemed to imply that the idea was to allow mixing with code under other licenses. But I must admit that's not a subject I've considered much.
In fact, I don't think I've ever seen any AGPL software that's grown a significant developer community.
It's... an extremely restrictive license, generally, and not one I'm comfortable using as an open-source developer. I know many others feel the same, which would lead to a lack of community, leading to a lack of community support, and potentially leading to the death of the product.