While the Raspberry Pi is not the perfect hacker-friendly computer, it has done a lot of good. Some reasons off the top of my head:
1. Providing a low cost computer has given many people access to computers. Giving more people access to the web, email, an office suit, a programming environment AND giving people the ability of safely tinker without the fear of bricking an expensive device.
2. Introduced many different types of people to the FOSS landscape of powerful tools (e.g. distros such as Debian, tools such as Python).
3. The Raspberry Pi foundation has paid developers to write/optimise FOSS (e.g. paid Collabora to optimise WebkitGTK+ -- I think some Wayland work was also done).
4. Built on top of existing FOSS tools (e.g. building Raspbian on top of Debian), instead of doing everything on their own in a proprietary fashion. This has no doubt also helped to introduce new people into these communities.
This is a really good counter-point to all the "locked down" (hacker unfriendly) devices like smart phones and tablets.