No, it's not a conspiracy thing, it's a human nature thing. People are going to invite people they know, and people know people through similar interests and ways of thought. While I'm not saying people are going to scrutinize invites to make sure they're not against their opinions, must of the people they invite will be people they know, who are biased to agree with them. The trend will not be absolute, of course, but it will be significant. As to why I would remove myself from the user pool, I have all of one hubwhell in the five months I've been here and feel no obligation to the community.
Please see my response to refugee. I like your suggestions here, so thank you, but I have to point out that as of right now, much of Hubski exists because people have invited their friends, acquaintances, co-workers etc to the site and I don't think it has suffered as a result. So, I don't quite buy in to the circle jerk theory. However, I am 100% with you in that I don't think we need to be actively turning interested people away. What I'm totally okay with is turning away people that would create an account, make a bunch of bullshit comments/posts for the ONE DAY they were here and never return.