I'm likely to have very different views than the norm on this subject. So take with a grain of salt.
1. In your own words, what is an ?indie? game?
No such thing. While the word "indie" is for independent(noted below). This I feel is a belittling reference. In context of language labelling any game/movie as indie is inappropriate. We don't for example call our local farmers, indie farmers, or local dairy as indie dairy. Though they "run" independently. So I don't believe any game is an indie game. Small developer game sure, but not indie. Technically even Electronic Arts at the the top is independent of any other organization.
2. Why do you think independent game developers join internet forums?
Inspiration, support, ideas, assisting the community.
3. Why do you think independent game developers leave internet forums?
jerks, and people who have closed minds, kicked out.
4. What are, in your opinion, the key limitations and benefits in regards to forum activity?
non really. I at this time don't feel of any key limits.
5. How do you think life in the forums affects the following ethical considerations: privacy and anonymity, intellectual property, people and machines, and digital citizenship? (Check the link below for descriptions on the preceding ethical considerations)
the internet has removed privacy.
the internet as removed anonymity
as for IP, if you share there is far less IP, but get in return feedback