When I use something from a distribution, I trust the distribution as organization. When I use something packaged by a developer, I trust the developer. I cannot verify thousands of developers, so I must trust the distribution and I can trust few developers or packagers outside of distribution.

Yes, but only for things you give access to (data files, internet)... sandboxing by default, it should not be able to do anything except consume CPU (memory needs to be limited also, which might be an issue in practice).