We (Twitter users) are not as much worried about our stream being polluted, as much as OUR tweets not being seen. Currently, as long as people are online, there's a certain guarantee that they will see it. You don't need to reach out for popularity, because they'll see it anyway. Once it becomes an algorithmically-defined popularity contest, it gets very similar to Facebook, something that most of die-hard twitter fans don't want this to be.
Yes, we think the 'algorithmic' feed is going to suck in terms of our streams, but also that our tweets will get lost in all the celebrity noise. Twitter reallllyyy doesn't seem to get that aspect of the complaints. This is more of a celeb-pandering move than to improve user experience.
So by giving my followers the option only see popularly selected tweets, you're already shutting them off me. Yeah, they may not always like my tweets, but they would like to see them once in a while (as I will want them to).
To summarize: We (existing twitter users) had a contract, an expectation-- that our timelines were going to be chronological, and we would see everything. Twitter is trying to change that, and changing our expectations WHILE we are using it. My guess is, it thinks the 'network effect' makes it too big to fail, and doing this will bring in more of the fb-crowd. By doing this, it is alienating us those who were here for precisely 'not-like-fb' features.
I am mad. Very mad. If this is made the default, this is going to be another 'google-killed-reader' rage.